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以下各组物质可做缓冲对的是
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N的氢化物（NH3）的熔点都比它同族中其他氢化物的熔点高得多，这主要由于NH3：
反应3A2++2B =3A+2B3+在标准状态下电池的电动势EΘ为1.8 V，某浓度时，反应的电池电动势E为1.6 V，则此时该反应的lgKΘ值为
已知H2O为弱场配体，CN－为强场配体。利用晶体场理论说明[Fe(H2O)6]3+和[Fe(CN)6]3–是低自旋配合物还是高自旋配合物，并写出中心原子的d电子排布
On average, American kids ages 3 to 12 spent 29 hours a week in school, eight hours more that they did in 1981. They also did more household work and participated in more of such organized activities as soccer and ballet (芭蕾舞). Involvement in sports, in particular, rose almost 50% from 1981 to 1997: boys now spend an average of four hours a week playing sports; girls log hall that time. All in all, however, children’s leisure time dropped from 40% of the day in 1981 to 25%“Children are affected by the same time crunch (危机) that affects their parents,” says Sandra Hofferth, who headed the recent study of children’s timetable. A chief reason, she says, is that more mothers are working outside the home. (Nevertheless, children in both double-income and “male breadwinner” households spent comparable amounts of time interacting with their parents 19 hours and 22 hours respectively. In contrast, children spent only 9 hours with their single mothers.)All work and no play could make for some very messed-up kids. “Play is the most powerful way a child explores the world and learns about himself,” says T. Berry Brazelton, professor at Harvard Medical School Unstructured play encourages independent thinking and allows the young to negotiate their relationships with their peers, but kids ages 3 to 12 spent only 12 hours a week engaged in it.The children sampled spent a quarter of their rapidly decreasing “free time” watching television. But that, believe it or not, was one of the findings parents might regard as good news. If they’re spending less time in front of the TV set, however, kids aren’t replacing it with reading. Despite efforts to get kids more interested in books, the children spent just over an hour a week reading. Let’s face it, who’s got the time?1. By mentioning “the same time crunch” (Line 1, Para. 2) Sandra Hofferth means ________.A) children have little time to play with their parentsB) children are not taken good care of by their working parentsC) both parents and children suffer from lack of leisure timeD) both parents and children have trouble managing their time2. According to the author, the reason given by Sandra Hofferth for the time crunch is ________.A) quite convincingB) partially trueC) totally groundlessD) rather confusing3. According to the author a child develops better if ________.A) he has plenty of time reading and studyingB) he is left to play with his peers in his own wayC) he has more time participating in school activitiesD) he is free to interact with his working parents4. The author is concerned about the fact that American kids ________.A) are engaged in more and more structured activitiesB) are increasingly neglected by their working mothersC) are spending more and more time watching TVD) are involved less and less in household work5. We can infer from the passage that ________.A) extracurricular activities promote children’s intelligenceB) most children will turn to reading with TV sets switched offC) efforts to get kids interested in reading have been fruitfulD) most parents believe reading to be beneficial to children
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