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动坐标系相对于静坐标系的运动称为牵连运动。
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在点的合成运动问题中，某瞬时动坐标系上一点的速度称为动点的牵连速度。
Section ADirections：In this section, there is a passage with ten blanks. You are required to select one word for each blank from a list of choices given in a word bank following the passage. Read the passage through carefully before making your choices. Each choice in the bank is identified by a letter. Please mark the corresponding letter for each item on Answer Sheet 2with a single line through the centre. You may not use any of the words in the bank more than once.There’re three main types of financial stress people encounter. The first type is apparent in people being stressed about the 26ups and downs of investment markets—actually not so much the ups, but 27the downs. These people are usually unable or unprepared to endure the long haul.The next common type of financial stress is that caused by debt. In a 28percentage of cases of debt-induced financial stress, credit cards and loans will be a central element. Often there’ll be a car loan and perhaps a mortgage, but credit cards often seem to be the gateway to debt-related financial difficulties for many.The third type of stress and 29the least known is inherited financial stress, which is the most destructive. It is experienced by those who have grown up in households where their parents regularly 30and fought about money. Money therefore becomes a stressful topic, and so the thought of sitting down and planning is an unattractive 31.Those suffering inherited financial anxiety 32to follow one of two patterns. Either they put their head in the sand: they would 33examining their financial statements, budgeting and discussing financial matters with those closest to them. Alternatively, they would go to the other 34, and micro-analyze everything, to the point of complete 35. They are convinced that whatever decision they make will be the wrong one.
Section BDirections：In this section, you are going to read a passage with ten statements attached to it. Each statement contains information given in one of the paragraphs. Identify the paragraph from which the information is derived. You may choose a paragraph more than once. Each paragraph is marked with a letter. Answer the questions by making the corresponding letter on Answer Sheet 2.Doctor’s Orders: Let Children Just Play[A] Imagine a drug that could enhance a child’s creativity and critical thinking. Imagine that this drug were simple to make, safe to take, and could be had for free. The nation’s leading pediatricians（儿科医生）say this miracle compound exists. In a new clinical report, they are urging doctors to prescribe it liberally to the children in their care.[B] “This may seem old-fashioned, but there are skills to be learned when kids aren’t told what to do,” said Dr. Michael Yogman, a Harvard Medical School pediatrician who led the drafting of the call to arms. Whether it’s rough physical play, outdoor play or social or pretend play, kids derive important lessons from the chance to make things up as they go, he said.[C] The advice, issued Monday by the American Academy of Pediatrics, may come as a shock to some parents. After spending years fretting（烦恼）over which toys to buy, which apps to download and which skill-building programs to send their kids to after school, letting them simply play—or better yet, playing with them—could seem like a step backward. The pediatricians insist that it’s not. The academy’s guidance does not include specific recommendations for the dosing of play. Instead, it asks doctors to advise parents before their babies turn two that play is essential to healthy development.[D] “Play is not silly behavior,” the academy’s report declares. It fosters children’s creativity, cooperation and problem-solving skills—all of which are critical for a 21st-century workforce. When parents engage in play with their children, it builds a wall against the harmful effects of all kinds of stress, including poverty, the academy says. In the pediatricians’ view, essentially every life skill that’s valued in adults can be built up with play. “Collaboration, negotiation, decision-making, creativity, leadership, and increased physical activity are just some of the skills and benefits children gain through play,” they wrote. The pediatricians’ appeal comes as kids are being squeezed by increasing academic demands at school and the constant invasion of digital media.[E] The trends have been a long time coming. Between 1981 and 1997, detailed time-use studies showed that the time children spent at play declined by 25 percent. Since the adoption of sweeping education reforms in 2001, public schools have steadily increased the amount of time devoted to preparing for standardized tests. The focus on academic “skills and drills” has cut deeply into recess（课间休息）and other time for free play.[F] By 2009, a study of Los Angeles kindergarten classrooms found that five-year-olds were so burdened with academic requirements that they were down to an average of just 19 minutes per day of “choice time,” when they were permitted to play freely with blocks, toys or other children. One in four Los Angeles teachers reported there was no time at all for “free play.” Increased academic pressures have left 30 percent of U.S. kindergarten classes without any recess. Such findings prompted the American Academy of Pediatrics to issue a policy statement in 2013 on the “crucial role of recess in school.”[G] Pediatricians aren’t the only ones who have noticed. In a report titled “Crisis in the Kindergarten,” a group of educators, health professionals and child advocates called the loss of play in early childhood “a tragedy, both for the children themselves and for our nation and world.” Kids in play-based kindergartens “end up equally good or better at reading and other intellectual skills, and they are more likely to become well-adjusted healthy people,” the Alliance for Childhood said in 2009. Indeed, new research demonstrates why playing with blocks might have been time better spent, Yogman said. The trial assessed the effectiveness of an early mathematics intervention（干预）aimed at preschoolers. The results showed almost no gains in math achievement.[H] Another playtime thief: the growing proportion of kids’ time spent in front of screens and digital devices, even among preschoolers. Last year, Common Sense Media reported that children up through age eight spent an average of two hours and 19 minutes in front of screens each day, including an average of 42 minutes a day for those under two. This increase of digital use comes with rising risks of obesity, sleep deprivation and cognitive（认知的）,language and social-emotional delays, the American Academy of Pediatrics warned in 2016.[I] “I respect that parents have busy lives and it’s easy to hand a child an iPhone,” Yogman said. “But there’s a cost to that. For young children, it’s much too passive. And kids really learn better when they’re actively engaged and have to really discover things.”[J] The decline of play is a special hazard for the roughly 1 in 5 children in the United States who live in poverty. These 14 million children most urgently need to develop the resilience（韧劲）that is cultivated with play. Instead, Yogman said, they are disproportionately affected by some of the trends that are making play scarce: academic pressures at schools that need to improve test scores, outside play areas that are limited or unsafe, and parents who lack the time or energy to share in playtime.[K] Yogman also worries about the pressures that squeeze playtime for more affluent kids. “The notion that as parents we need to schedule every minute of their time is not doing them a great service,” he said. Even well-meaning parents may be “robbing them of the opportunity to have that joy of discovery and curiosity—the opportunity to find things out on their own.”[L]Play may not be a hard sell to kids. But UCLA pediatrician Carlos Lerner acknowledged that the pediatricians’ new prescription may meet with skepticism（怀疑）from parents, who are anxious for advice on how to give their kids a leg up in the world. They should welcome the simplicity of the message, Lerner said. “It’s liberating to be able to offer them this advice: that you spending time with your child and letting him play is one of the most valuable things you can do,” he said. “It doesn’t have to involve spending a lot of money or time, or joining a parenting group. It’s something we can offer that’s achievable. They just don’t recognize it right now as particularly valuable.”36. Increased use of digital devices steals away children’s playtime.37. Since the beginning of this century, an increasing amount of time has been shifted in public schools from recess to academic activities.38. It has been acknowledged that while kids may welcome pediatrician’s recommendation, their parents may doubt its feasibility.39. According to some professionals, deprivation of young children’s playtime will do harm not only to children themselves but to the country and the world.40. By playing with children, parents can prevent them from being harmed by stress.41. Playing with digital device discourages kids from active discovery, according to pediatrician Dr. Michael Yogman.42. The suggestion of letting children simply play may sound like going backwards to parents who want to help build their children’s skills.43. Dr. Michael Yogman believes the idea that parents should carefully schedule children’s time may not be helpful to their growth.44. One quarter of teachers in an American city said that children in kindergartens had no time for playing freely.45. According to a pediatrician, no matter what kind of play children engage in, they are learning how to create things.
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