Do you know why different animals or pests have their special colors? Colors in them seem

Do you know why different animals or pests have their special colors? Colors 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 colors together with the change of the colors of crops. When crops are green, locusts look green. But as the harvest time es, locusts change to the same brown color as crops have. Some other pests with different colors 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 coloring is protecting themselves. Bears, lions and other animals move quietly through forests. They cannot be seen by hunters. This is because they have the colors 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 spread 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.
根据短文内容, 指出能完成所给句子或回答所提问题的最佳答案。
【小题1】From the passage we learn that locusts      .A．are small animalsB．are easily found by birdsC．are dangerous to their enemiesD．change their colors to protect themselves【小题2】Bears and lions can keep safe because they      .A．have the colors much like the treesB．move quicklyC．like brown and grey colorsD．live in forests【小题3】The kind of fish live up to now because      .A．it is very big and strongB．the liquid it sends out help it escape from its enemiesC．the liquid it sends out can kill its enemiesD．it swims faster than any other fish【小题4】Which is the best title for this passage?A．The Change of Colors for Animals and PestsB．Colors of Different Animals and PestsC．The Main Use of Colors for Animals and PestsD．Some Animals and PestsD