作业精灵老师示例：Last Sunday, Sam and Bobby are playing table tennis happily in the park.
Sam is really good at table tennis. Billy and Willy cheer for them loudly.Sam is too excited and he
hits the ball hard. Then, they cannot find the ball. Finally, Sam and Bobby see a hole in the ground.
Sam has an idea.He brings some water quickly and pours it into the hole. And they find many balls
in the hole.
