A、Because we feel that we have become mature. B、Because laughter is the best medicine. C、Because we understand the world around

We start to find things laughable--or not laughable early in life. A baby first smiles when he is about eight days old. Many scientists believe he smiles because he finds simple pleasure around him-food, warmth and comfort. When the baby grows to the age of six months, he begins to learn to laugh for the same reason he is going to laugh for in the rest of his life. He laughs because he thinks he can overcome some trouble. When a father throws his child into the air, the child probably won’t laugh at the beginning. How does he know Daddy will catch him? Once the child realizes he will be caught, he is free to enjoy his flying. Then he will begin to laugh. When we grow old we may laugh on many occasions. But we usually laugh for the same reason. Laughing is helpful to us because it can make us excited. And we can always deal with things better when we are excited.