The fiddler crab (蟹) is a living clock. It indicates the time of day by the colour of its skin, which is dark by day and pale by night. The crab’s changing colour follows a regular twenty-four hour plan that exactly matches the daily rhythm of the sun.
Does the crab actually keep time, or does its skin simply answer to the sun’s rays, changing colour according to the amount of light which strikes it? To find out, biologists kept crabs in a dark room for two months. Even without daylight, the crab’s skin colour continued to change exactly on time.
This characteristic probably developed gradually in answer to the daily rising and setting of the sun, to help protect the crab from sunlight and enemies. After millions of years it has become completely controlled inside the living body of the crab.
The biologists noticed that once each day the colour of the fiddler crab is especially dark, and that each day this happens fifty minutes later than on the day before. From this they discovered that each crab follows not only the rhythm of the sun but also that of the tides (潮水). The crab’s period of greatest darkening is exactly the time of low tide on the beach where it was caught!
40. The crab’s changing colour _______.
A. tells the crab what time it is
B. protects the crab from the sunlight and enemies
C. keeps the crab warm
D. is of no real use
41. When the fiddler crabs were kept in the dark, they _______.
A. did not change colour B. changed colour more quickly
C. changed colour more slowly D. changed colour on the same timetable
42. The crab’s colour—changing ability was probably developed _______.
A. in the process of evolution (进化) B. over millions of years
C. by the work of biologists D. both A and B
43. The best title for this selection would be _______.
A. The Sun and the Tides B. Discoveries in Biology
C. A scientific Study D. A Living Clock
答案
40---43 BDDD
考点名称：科教类阅读
科教类阅读的概念：
科教类阅读主要考查考生对书面语篇的整体领悟能力和接受及处理具体信息的能力。试题的取材，密切联系当前我国和世界经济、科技等方面的变化，有关数据的来源真实可信。
科教类文章阅读技巧：
一、材料特点：
这类文章的总体特点是：科技词汇多，句子结构复杂，理论性强，逻辑严谨。具体说来它有以下几个特点：
1、文章中词汇的意义比较单一、稳定、简明，不带感情色彩，具有单一性和准确性的特点。这类文章通常不会出现文学英语中采用的排比、比喻、夸张等修辞手法，一词多义的现象也不多见。
2、句子结构较复杂，语法分析较困难。为了描述一个客观事物，严密地表达自己的思想，作者经常会使用集多种语法现象于一体的长句。
3、常使用被动语态，尤其是一些惯用被动句式。
二、命题特点：
科普类阅读的主要命题形式有事实细节题、词义猜测题、推理判断题以及主旨概括题等，其中推理判断题居多。
三、应对策略：
1、要想做好科普英语阅读理解题，同学们就要注意平时多读科普知识类文章，学习科普知识，积累常见的科普词汇，从根本上提高科普英语的阅读能力。
2、要熟悉科普类文章的结构特点。科普类文章一般由标题(Head line)，导语(Introduction)，背景(Back ground)，主体(Main body)和结尾(End)五部分构成。标题是文章中心思想高度而又精辟的概括，但根据历年的高考情况来看，这类阅读理解材料一般不给标题，而要同学们选择标题。导语一般位于整篇文章的首段。背景交待一个事实的起因。主体则对导语概括的事实进行详细叙述，这一部分命题往往最多，因此，阅读时，同学们要把这部分作为重点。结尾往往也是中心思想的概括，并与导语相呼应，命题者常在此要设计一道推理判断题。
3、在进行推理判断时，同学们一定要以阅读材料所提供的科学事实为依据，同时所得出的结论还应符合基本的科普常识。