题目内容
新一期《科学》杂志说，康奈尔大学的科学家把一部微型马达与一个金属螺旋桨组装在一起，使螺旋桨能够以8转/秒的速度旋转。该大学生物工程教授蒙泰马尼奥说：“这是一台真正的纳米机器，”这台马达是从给细胞提供能量的分子中获得能量的，所以他认为科学家终将能够制造出比细菌还小的机器人。它们将能够修复细胞损伤，制造药物并且攻击癌细胞。他说：“这为制造在细胞中运转的机器打开了大门。这将使我们把设计好的装置与生命系统融合起来”。划线的句子中“这”指代的对象是( )。
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A. evaporation B. water cycle C. Complicated process D. ever-going-on process E. rainfall F. ground water G. vapor H. transpiration I. high land J. formation of clouds K. formation of rain L. cold air M. drops of rain N. absorbed by soil O. porous rock layer P. non-porous rock layer Q. accumulation of water R. process of water cycle 水循环过程( ) 降 雨( )
某一运输公司搬货物，如用甲车队需要6个小时，乙车队则需要12个小时，两车队一起干了2小时后，甲车队临时有任务，剩下的由乙车队负责，那么乙车队还要做几个小时才能完成任务
Instead of (wait) _________ for the teacher to explain, you should try your best first.
As people continue to grow and age, our body systems continue to change. At a certain point in your life your body systems will begin to weaken. Your strength may become weaker. It may become more difficult for you to see and hear. The slow change of aging causes our bodies to lose some of their ability to bounce back from disease and injury. In order to live longer, we have always tried to slow or stop this change that leads us toward the end of our lives. Many factors decide your health. A good diet plays an important role. The amount and type of exercise you get is another factor. Your living condition is yet another. But scientists studying aging problem want to know: Why do people grow old They hope that by studying the aging medical science they may be able to make the length of life longer. There is nothing to be afraid of as old age comes. Many consider the later part of life to be the best time for living. Physical activity may become less, but often you get better understanding of yourself and the world. What we consider old age now may only be middle age some day soon. Who knows, with so many advances in medical science happening so quickly, life span may one day be measured in centuries, rather than in years. According to the passage, "span" means ______.
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