题目内容：

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 are very fond of locusts (蝗虫), but birds can’t easily catch locusts because locusts change their colours together with the change of the colour of crops. When crops are green, locusts look green. But when crops are ripe, 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 them. Bears, wolves and other beasts move quietly through forests. They are usually invisible(can’t be seen) to the eyes of hunters, because they have the colour much like the bark（树皮）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 up to now though it is not powerful at all.

1. This passage mainly talks about _______.

A. the change of colour in locusts

B. animals or pests can dye（染色）themselves different colours

C. how a certain sea fish protects itself

D. the protective colour of animals and pests

2. Locusts are pests but they aren’t easily wiped out by their enemies because _______.

A. they change colors with the crops

B. they are dangerous to their enemies

C. they fly very fast

D. they are powerful enough

3.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

4.A certain fish living in seas has lived through millions of year because _______.

A. it is the most powerful in the sea

B. no other fishes can swim as fast as it can

C. it can send out a kind of liquid which makes its enemies unable to find it

D. the liquid it sends out can kill its enemies