Do you know why different animals or pests（害虫）have their special colours? Colours in them seem to be used mainly to protect themselves.
Some birds like eating locusts, but birds cannot easily catch them. Why? It is because locusts change their colours together with the change of the colours of crops. When crops are green, locusts look green. But as the harvest time comes, locusts change to the same brown colour as crops have. Some other pests with different colours from plants are easily found and eaten by others. So they have to hide themselves for lives and appear only at night.
If you study the animal life, you’ll find the main use of colouring is protecting themselves. Bears, lions and other animals move quietly through forests. They cannot be seen by hunters. This is because they have the colours much like the tree.
Have you ever noticed an even more strange act? A kind of fish in the sea can send out a kind of very black liquid when it faces danger. While the liquid spreads over, the enemies cannot find it. And it immediately swims away. So it has lived up to now though it isn’t strong at all.
From the passage we can learn that locusts _______．

A．are small animals

B．are easily found by birds

C．are dangerous to their enemies

D．change their colours to protect themselves

Bears and lions can keep safe because they_______.

A．have the colours much like the trees

B．move quickly

C．like brown and grey colours

D．live in forests

Why can the fish mentioned in the last paragraph live up to now?

A．Because it is very strong.

B．Because the liquid it sends out can help it get away from its enemies.

C．Because the liquid it sends out can kill its enemies.

D．Because it swims faster than any other fish.

Which is the best title for this passage?

A．The Change of Colours for Animals and Pests

B．Colours of Different Animals and Pests

C．The Main Use of Colours for Animals and Pests

D．Some Animals and Pests