问题 问答题 论述题

两侧对称出现的意义是什么?

答案

参考答案:从扁形动物开始出现了两侧对称的体型,从动物演化上看,这种体型主要是由于动物从水中漂浮生活进入到水低爬行生活的结果。已发展的这种体型对动物的进化具有重要的意义,因为凡是两侧对称的动物,其体可明显的分出前、后,左、右,背、腹,体背面发展了保护的功能;腹面发展了运动的功能,向前的一端总是首先接触新的外界条件,促进了神经系统和感觉器官越来越向前端集中,逐渐出现了头部,使得动物由不定向运动变为定向运动;使动物的感应更为准确、迅速而有效;使其适应的范围更广泛,两侧对称不仅适用于游泳,又适于爬行,从水中爬行,才有可能进化到陆地上爬行。因此,两侧对称是动物由水生发展到陆生的重要条件。

阅读理解

When you walk along a street in a big city in the United States, you may see clocks in most stores. Radio announcers give the correct time during the day. People there think that it is important to know the time. Most Americans have watches. They want to do certain things at certain times. They do not want to be late. Not all people all over the world value time. Suppose you visit a certain country in South America. You would find that people living there do not like to rush. If you had an appointment(约会)with someone, he would probably be late. He would not care for arriving on time. In some countries in South America, even the radio programs may not begin right on time, nor do the radio announcers think it important to announce the right time. Many people regard a clock as a machine. It seems to them that a person who does everything on time is controlled(控制)by a machine. They do not want a clock or any machine to have that much power over their lives.

小题1:There are clocks in most stores in the US cities because ______.

A.people in the stores want to sell these clocks

B.people think it important to know the time

C.bosses want to make their stores beautiful

D.they needn't wear watches when they are away from home小题2:The underlined word “rush” in the passage most probably means ______.

A.“run”

B.“race”

C.“move”

D.“hurry”小题3:If you had an appointment with someone in some place in South America,he might not arrive on time,and this is because ______.

A.he didn't have a watch with him

B.he didn't think it important to arrive on time

C.he forgot to have a look at a watch or a clock

D.he didn't like an appointment with someone小题4:In some countries in South America ______.

A.the radio programs many start a bit early or late

B.the radio announcers do think it important to announce the exact time

C.many people think a clock has much power

D.most people do not want to be controlled by others

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