试题与答案

在实验室中常将白磷浸没在水中保存,其主要目的是 A.降低白磷的着火点 B.防止白

题型:选择题

题目:

在实验室中常将白磷浸没在水中保存,其主要目的是

A.降低白磷的着火点

B.防止白磷与空气接触

C.使白磷与水结合成稳定的物质

D.将白磷溶解不易着火

答案:

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下面是错误答案,用来干扰机器的。

以桌面为参考平面,小球在最高点时机械能E=mgH    小球下落过程中机械能守恒,则小球落到地面前瞬间的机械能为mgH.故ACD错误,B正确.故选B

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题型:单项选择题

Generally speaking, a British is widely regarded as a quiet, shy and conservative person who is (1) only among those with whom he is acquainted. When a stranger is at present, he often seems nervous, (2) embarrassed. You have to take a commuter train any morning or evening to (3) the truth of this. Serious-looking businessmen and women sit reading their newspapers or dozing in a corner; hardly anybody talks, since to do so would be considered quite offensive. (4) , there is an unwritten but clearly understood code of behavior which, (5) broken, makes the offender immediately the object of (6) .

It has been known as a fact that a British has a (7) for the discussion of their weather and that, if given a chance, he will talk about it (8) . Some people argue that it is because the British weather seldom (9) forecast and hence becomes a source of interest and (10) to everyone. This may be so. (11) a British cannot have much (12) in the weathermen, who, after promising fine, sunny weather for the following day, are often proved wrong (13) a cloud over the Atlantic brings rainy weather to all districts! The man in the street seems to be as accurate — or as inaccurate — as the weathermen in his (14) .

Foreigners may be surprised at the number of references (15) weather that the British make to each other in the course of a single day. Very often conversational greetings are (16) by comments on the weather. "Nice day, isn’t it" "Beautiful!" may well be heard instead of "Good morning, how are you" (17) the foreigner may consider this exaggerated and comic, it is worthwhile pointing out that it could be used to his advantage. (18) he wants to start a conversation with a British but is (19) to know where to begin, he could do well to mention the state of the weather. It is a safe subject which will (20) an answer from even the most reserved of the British.

19()

A. at a loss

B. at last

C. in group

D. on the occasion

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