Have you wondered why different animals or pests have their particular colours? Colours in them seem to be used mainly to protect themselves.
Birds, especially seagulls（海鷗） are very fond of locusts（蝗蟲(chóng)）, but birds can’t easily catch locusts because locusts change their colours together with the change of the colour of crops（莊稼）. When crops are green, locusts look green. But when crops are ripe（成熟的）, locusts take on exactly the same brown colour as crops have. Some other pests with different colours from plants are usually easily found and eaten by their enemies. So they have to hide themselves in terror for lives and appear only at night.
If you study the animal life in any part of the world, you will find the main use of colouring is to protect themselves, bears, wolves and other beasts move quietly through forests. They are usually invisible to the eyes of hunters, because they have the colour much like the barks(樹(shù)皮) of trees.
An even more strange act remains to be noticed. A kind of fish living in seas can send out a kind of very black liquid when it faces danger. While the liquid is over, its enemies cannot find it, and it quickly swims away. Thus,it has existed（存活）up to now though it is not powerful at all.
1.This passage mainly talks about ______.
A. the change of colour in locusts
B. the protective colouration of animals and pests
C. how a certain sea fish protects itself
D. animals or pests can dye themselves different colours
2.The pests that have different colours from plants usually appear at night because ______.
A. their enemies can easily find them and eat them
B. they have the habit of coming out in darkness
C. it’s easy for them to destroy plants in darkness
D. birds take their rests when night comes
3.What does the word “invisible” in Paragraph 3 mean?
A. Can’t be seen B. Can be seen
C. Can’t move D. Can’t change
