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风险的变动常常可以用标准方差来表示。一般说来，标准方差越大，各种可能收益的分布就越集中，投资风险也就越小。 ()
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Just as bodies require more maintenance with the passing years, so do brains, which scientists now know show signs of aging as early as the 20s and 30s. "Brain aging starts at a very young age, younger than any of us had imagined and these processes continue gradually over the years," said Dr. Gary Small, the director of the Center on Aging at the University of California, Los Angeles. "I'm convinced that it is never too early to get started on a mental or brain-fitness program," he added.
In his book, The Memory Bible, the 51-year-old neuroscientist (神经学家) lists what he refers to as the 10 suggestions for keeping the brain young. They include training memory, building skills, reducing stress, mental exercises; brain food and a healthy lifestyle. It's a game plan for keeping brain cells sparking and neural networks in perfect shape.
"Misplacing your keys a couple of times don't mean you should start labeling your cabinets. Memory loss is not an inevitable consequence of aging. Our brains can fight back," he said.
Small provides the weapons for a full-scale attack.
Simple memory tests give an indication of what you are up against and tools such as "look" and "connect" are designed to make sure that important things such as names and dates are never forgotten. "So if you wanted to learn names and faces, for example, you meet Mrs. Beatty and you notice a distinguishing facial feature, maybe a high eyebrow," said Small. "You associate the first thing that comes to mind. I think of the actor Warren Beatty so I create a mental picture of Warren Beatty kissing her brow."
Small admits it may sound a bit strange but he says it works. "Mental exercises could be anything from doing crossword puzzles and writing with your left hand if you are right handed or learning a language. It could be anything that is fun that people enjoy doing," he added.
He also recommends physical exercise, a low-fat diet and eating foods rich in fatty acids, such as fish, nuts, and fruits and vegetables high in antioxidants (抗氧化剂) including blueberries and onions in addition to reducing stress.
The "mad moment" in the first paragraph refers to the time when we ______.
The parents were much kinder to their youngest child than they were to the others, ______,
Similarly, college classroom space should be designed to encourage the activity of critical thinking. We will move into the twenty-first century, but step into almost any college classroom and you will step back in time at least a hundred years. Desks are normally in straight rows, so students can clearly see the teacher but not all their classmates. The assumption behind such an arrangement is obvious: Everything important comes from the teacher.
With a little imagination and effort, unless desks are fixed to the floor, the teacher can correct this situation and create space that encourages interchanges among students. In small or standard-size classes, chairs, desks and tables can be arranged in different ways: circles, U-shapes, or semicircles. The primary goal should be for everyone to be able to see everyone else. Larger classes, particularly those held in lecture halls, unfortunately, allow much less flexibility.
Arrangement of the classroom should also make it easy to divide students into small groups for discussion or problem-solving exercises. Small classes with moveable desks and tables present no problem. Even in large lecture halls, it is possible for students to turn around and form. groups of four to six. Breaking a class into small groups provides more opportunities for students to interact with each other, think out hard, and see how other students' thinking processes operate all these are the most important elements in developing new modes of critical thinking.
In course that regularly use a small group format, students might be asked to stay in the same small groups throughout the course. A colleague of mine allows students to move around during the first two weeks, until they find a group they are comfortable with. He then asks them to stay in the same seat, with the same group, from then on. This not only creates a comfortable setting for interaction but helps him learn students' names and faces.
The expression "step back in time at least a hundred years" (Para.2) is intended to convey the idea that
By saying "I think of the actor Warren Beatty so I create...her brow", Dr. Small is trying
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