问题 单项选择题

心房和心室收缩在时间上不重叠,后者必定落在前者完毕后的原因是

A.窦房结到心房距离近,而到心室距离远

B.心房肌传导速度快,心室肌传导速度慢

C.房室交界处传导速度慢而形成房—室延搁

D.窦房结分别通过不同传导通路到达心房和心室

答案

参考答案:C

解析: 生理情况下,窦房结的兴奋传导到心室必须经过房室交界,而房室交界区细胞的传导速度很慢,其中又以结区为最慢,因此兴奋由窦房结传至心室相对于心房要慢,需经一个时间延搁,这一现象称为房—室延搁。所以心房和心室收缩在时间上不重叠,后者必定落在前者完毕后。

选择题
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