A large number of animals use their colours to blend into the environment. Colours in them seem to be used mainly to ________ themselves.

Some birds like eating locusts(蝗虫), but birds cannot catch them ________. Why? It is because locusts change their colours together ________ the change of the colours of crops. When crops are green, locusts look green. But as the harvest time comes, locusts change to the ________ brown colour as crops have. Some other pests(害虫) with different colours from plants are easily ________ and eaten by others. So they have to hide themselves for lives in the ________ and come out only at night.

Bears, lions and other animals move quietly ________ forests. They cannot be easily seen by hunters. This is ________ they have the colours much like the trees.

Have you ever noticed an even ________ act of animals? A kind of fish in the sea can send out a kind of black liquid(液体) when it ________ danger. While the liquid spreads over(散开), its enemies(敌人) cannot find it. And it immediately swims away. So it has lived up to now though it is not strong at all.

Mark, Sue and Ann are my three best fiends. Mark, Sue and I go to the same school and we are all classmates. Mark is one of the tallest boys in our class. He is even taller than our English teacher, Mr. Black. When I feel sad, Mark always tells funny jokes and makes me happy again. Sometimes he pulls a funny face and makes me laugh until my stomach hurts.

Sue, on the other hand, is very gentle and kind. She is not as loud or funny as Mark, but she is helpful and generous. I can always talk to her about my problems. She is a good listener and she is really smart. She said she would like to be a good doctor when she grows up.

Ann, another good friend of mine, is from the USA. She is my online friend. Although(尽管) we do not see each other very often, I still think of her as one of my best friends. We talk on the Internet as much as we can and I often tell her about my school, my friends and my family. I like to share my joy with her. Ann is a true friend. She is honest and always tells me her opinions(观点) about things.