问题 填空题

填空:

(1)把一个图形绕着某一个点旋转180°,如果它能够与另一个图形______,那么就说这两个图形关于这个点对称或中心______,这个点叫做______中心,这两个图形中的对应点叫做关于中心的______点.

(2)中心对称的性质有:中心对称的两个图形是______图形;中心对称的两个图形,对称点所连线段都______对称中心,而且被对称中心所______.

答案

(1)中心对称的定义:把一个图形绕着某个点旋转180°,如果它能够与另一个图形重合,那么就说这两个图形关于这个点对称或中心对称,这个点叫做对称中心,这两个图形中的对应点叫做关于中心的对称点.

(2)中心对称的性质:①关于中心对称的两个图形能够完全重合;

②关于中心对称的两个图形,对应点的连线都经过对称中心,并且被对称中心平分.

故答案为:重合、对称、对称、对称;全等、经过、平分.

阅读理解

III.  Reading comprehension: (40%)

A

For every five men in the Civil War who died in battle , two or three died of disease. Doctors of that time knew very little about causes of sickness or ways of preventing it. Thousands of men in poor health became soldiers. Many of them could not resist epidemic (瘟疫)diseases that went through the places where they lived .

Army life was hard. Soldiers got little fruit or vegetables. There was no milk unless they happened to find a cow. Neither their clothes nor their living places protected the troops from rain, snow, and cold . Sickness and disease were spread by insects , rats , and unclean drinking water . Often the men drank straight from muddy streams .

Gunshot wounds were serious, as in any war, but they did not cause as many deaths as disease did.

1. Disease caused ___.                                                    

A.only a few deaths  B.fewer deaths than wounds did

C.more deaths than wounds did   D.both A and B

2.Men who were accepted as Civil War soldiers were ______.       

A.known to have already had some epidemic diseases

B.required to be in perfect health

C.able to resist epidemic disease easily   D.sometimes in poor health

3.Army life was hard for troops because ______          

A.the place where they lived didn't keep them safe from bad weather

B.they had no warm clothing

C.they seldom had good, healthful food   D.all of the above

4.Insects and rats were dangerous because they ______      

A.destroyed food  B.carried diseases

C.made the water unclean  D.tore the soldiers' clothes into pieces

5.The best title for this selection is ______.          

A.The Cause of Disease  B.The Greatest Danger in the Civil War

C.Insects, Rats, and Gunshot Wounds  D.The History of Epidemic Disease  

判断题