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问题 选择题

（理）如图所示的皮带传动装置中，O为轮子A和B的共同转轴，O′为轮子C的转轴，A、B、C分别是三个轮子边缘上的质点，且RA＝RC＝2RB，则三质点的向心加速度大小之比aA∶aB∶aC等于

A．4∶2∶1

B．2∶1∶2

C．1∶2∶4

D．4∶1∶4

答案

答案：A

题目分析：根据题意设a的半径为2，则C的半径为2，B的半径为1，根据，可以求出，，则根据可知，正确答案为A

点评：本题考查了向心加速度的计算，包括线速度、角速度的计算。

单项选择题

男性，62岁，休息时反复发作胸痛，发作时心电图示广泛sT段抬高，胸痛缓解时心电图正常，应首先考虑的诊断是（）

A.劳力性心绞痛

B.变异性心绞痛

C.急性心肌梗死

D.主动脉夹层

E.肺动脉栓塞
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单项选择题

The following questions present a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.

These questions test correctness and effectiveness of expression. In choosing your answer, follow the requirements of standard written English; that is, pay attention to grammar, choice of words, and sentence construction. Choose the answer that produces the most effective sentence; this answer should be clear and exact, without awkwardness, ambiguity, redundancy, or grammatical error.

The stock market collapse of 1929 had far-reaching consequences for the national economy, causing a nationwide collapse in home values, putting millions out of work, and by erasing the investment savings of one-fifth of the population.（）

A. and by erasing

B. and erasing

C. and having erased

D. and erased

E. by erasing
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