题干

已知结构为正四面体型的离子A和直线型离子B反应,生成三角锥形分子C和V形分子D(A、B、C、D均为10电子微粒,组成它们的元素原子序数均小于10),下列说法正确的是(  )

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A:分子C与D不能发生化学反应

B:微粒A的空间结构与CH4相似,它们均为正四面体,所以A是非极性分子

C:固态D的熔沸点明显高于固态H2S的原因在于D分子中的共价键强于S﹣H键

D:在25℃时,A的盐酸盐溶液的pH小于7

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D

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    Grown­ups are often surprised by how well they remember something they learned as children but have never practiced ever since. A man who has not had a chance to go swimming for years can still swim as well as ever when he gets back in the water. He can get on a bicycle after many years and still ride away. He can play catch and hit a ball as well as his son. A mother who has not thought about the words for years can teach her daughter the poem that begins “Twinkle, twinkle, little star” or remember the story of Cinderella or Goldilocks and the Three Bears.

    One explanation is the law of overlearning, which can be stated as follows: Once we have learned something, additional learning trials(尝试)increase the length of time we will remember it.

    In childhood we usually continue to practice such skills as swimming, bicycle riding, and playing baseball long after we have learned them. We continue to listen to and remind ourselves of words such as “Twinkle, twinkle, little star” and childhood tales such as Cinderella and Goldilocks. We not only learn but overlearn.

    The multiplication tables(乘法口诀表)are an exception to the general rule that we forget rather quickly the things that we learn in school, because they are another of the things we overlearn in childhood.

    The law of overlearning explains why cramming(突击学习)for an examination, though it may result in a passing grade, is not a satisfactory way to learn a college course. By cramming, a student may learn the subject well enough to get by on the examination, but he is likely soon to forget almost everything he learned. A little overlearning, on the other hand, is really necessary for one's future development.