题目

Do you know why different animals or pests（昆虫） have their special colors? Colors in them seem to be used mainly to protect themselves. Some birds like eating locusts(蝗虫)，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 comes, 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 2块砖重10千克，100块砖重 千克， 块砖重1吨．