18．It is one of the greatest mysteries of nature．In case you haven't noticed，all living things follow very definite，individual rhythms，all as regular as a clock，but what makes them regular？
Though many scientists maintain that these rhythms are the result of some outside force like gravity or radiation or both，the results of most scientific researches agree with other scientists who believe that each living thing has its own built-in biological"time clock．"
Take the mystery of migration for example．Scientists can't really explain why many species of birds migrate in the autumn even though the temperature is still summery．The birds just seem to snub the comfortable weather that they are having．When a certain time comes，they travel south by the thousand．In spring time，they migrate northwards even though there probably is snow still covering the ground when they finally arrive．Something said"go，"and they did．
Animals that hibernate （冬眠） are obeying individual time clocks，too．When their clock indicates the time to take a winter's nap，they do，and nothing can stop them．At a certain time in the spring，they wake up and come out regardless of the weather outside．
Plants appear to have yearly rhythms，such as the sprouting of seeds，and they also have daily rhythms．Notice sometimes that plants raise their leaves in daylight and lower them at night．
If you live along the California coast，you can easily observe a demonstration of this mysterious clock functioning regularly．There，from February to September，the highest tides occur exactly every fourteen and four-fifths days，and during these high tides，but at no other time，small silvery fish called grunions surf-ride a wave to the beach．There the female deposits her eggs in the sand and the male fertilizes them； then both hitch a wave-ride back to the sea．Exactly fourteen and four-fifths days later，never before or after，the tiny eggs hatch，and the high tide carries the new babies out to sea．
72．According to the passage，the mysterious rhythms result fromD．
A．the influence of gravity on living species
B．the effect of radiation on living species
C．the influence of a mysterious outer force on living species
D．the internal mechanism inside the living species
73．The underlined word"snub"in the third paragraph probably meansB．
A．fight B．ignore C．symbolize D．criticize
74．Which of the following statements is NOT TRUE？D
A．Hibernating animals are obeying an internal time clock．
B．The positioning of the leaves of some plants is due to the daily rhythms．
C．The internal clock functioning is demonstrated in the reproducing habits of grunions．
D．The yearly hibernation is more because of the weather influence than the biological functioning．
75．The passage is mainly aboutA．
A．the rhythms of life
B．the reasons of mysterious hibernation
C．strange behaviors of species
D．the timing for different events in the world of species．
分析 本文主要讨论的是地球上生命的节奏，不同的物种有不同的生长规律，有不同的生活节奏，其实是由于其体内的内在机制所决定的．
解答 72----75 D B D A
72．D 根据Though many scientists maintain that these rhythms are the result of some outside force like gravity or radiation or both，the results of most scientific researches agree with other scientists who believe that each living thing has its own built-in biological"time clock．"可知，生物身上的节奏是由于其体内的生物机制所决定的，故答案为D
73．B 根据The birds just seem to snub the comfortable weather that they are having．When a certain time comes，they travel south by the thousand．可知，候鸟不管天气如何，只要到了某个时间就会迁徙，故答案为B
74．D 根据 Animals that hibernate （冬眠） are obeying individual time clocks，too．When their clock indicates the time to take a winter's nap，they do，and nothing can stop them．At a certain time in the spring，they wake up and come out regardless of the weather outside．可知，动物冬眠主要不是根据天气，而是根据的内在的生物钟，故答案为D
75．A 纵观全文，可知本文主要讨论的是地球上生命的节奏，不同的物种有不同的生长规律，有不同的生活节奏，其实是由于其体内的内在机制所决定的，故答案为A
点评 做阅读时经常犯错的主要原因是，仅凭读过文章后残留在脑海中的一丝印象来勾选答案，这样便很容易掉入出题人故意设布下的题目陷阱．所谓阅读理解，对于题目的理解一定要忠实于原文，因此，每一道题都应该与原文作全面的对比与核查，再得出答案．也就是说，阅读理解的每一道题目，在原文都应该有明确的出处，我们把这一出处叫做原文相关句，（1）排除与原文相关句主题不一致的选项（2）排除与原文相关句态度相反的选项 （3）排除用于过于极端或负面的选项（4）注意结合文章主旨和主题去排除．
