下列四个命题：①一组对边平行，另一组对边相等的四边形是等腰梯形；②对角线互相垂直且相等的四边形是正方形；③顺次连接菱形各边中点所得四边形是矩形；④等腰三角形腰上的高与中线重合。其中真命题有
A．1个
B．2个
C．3个
D．4个
答案：A
题目分析：①一组对边平行，另一组对边相等的四边形可能是等腰梯形，也可能是平行四边形；②对角线互相垂直且相等的四边形可能是正方形，也可能是等腰梯形；③顺次连接菱形各边中点所得四边形是矩形，因为菱形的对角线互相垂直，顺次连接菱形各边中点构成的四边形的边都与菱形的对角线平行，所以所得的四边形的相邻的两边是互相垂直的，四个角都是直角的四边形是矩形；④等腰三角形底边上的高与中线重合。所以只有③正确，是真命题
点评：本题考查平行四边形的判定，考生掌握平行四边形的判定方法是解答本题的关键
| 完形填空 | ||||
| Certainly dustmen prefer to be known as "Reuse Collection and Disposal Officers". You may think that this is rather 1 , and it is better to call a spade a spade. But dustmen can be as 2 as people of any other occupation, though we must 3 that their job is not a 4 one in the world. We often take dustmen for granted. Perhaps because they usually come very early in the morning, before most people are 5 .We are likely to forget their 6 .Our dustbins are 7 regularly, but we 8 stop to think about the men who do this. However, it is one of the most important jobs in the world, and when there are no dustmen to 9 the rubbish, the general 10 soon becomes aware that something is wrong. Recently, the dustmen of England went on strike for higher wages. During the first few days it was regarded as a 11 .But when the first two weeks had passed, and the dustbins were overflowing in nearly every backyard in the country, the joke did not seem so 12 any more. 13 the strike continued, people could not 14 the hills of rubbish around their dustbins, and they looked for other places in which to 15 it. Even Leicester Square, in the heart of West End of London, was 16 high with plastic bags full of smelly rubbish. This was a(n) 17 attraction that the people of London were not at all 18 to see. Even when the strike was over, it took several weeks for the country to get cleaned up completely. Perhaps now the English people appreciate the work of 19 dustmen rather more 20 and won't take them for granted any more. | ||||
|