根据短文内容，回答下列问题。

    There were two birds living in a tree. Later, they had three little baby birds. They brought fat worms (虫子)to the mouth of the baby birds. But there was a problem. One of the little birds, Jimmy, was always hungry. He ate and ate. Soon he became very fat.

    One day the mother birds told the three children to learn to fly. Jimmy's sisters learnt fast. It was Jimmy's turn. Jimmy did as his mother told him to fly. But he was too fat. He couldn't learn to fly. His mom was very worried. She stopped giving Jimmy food to eat. She decided that Jimmy must lose weight. After much effort (努力) Jimmy could fly. He could learn how to find worms to eat. And the whole family lived happily.