作业精灵老师示例：
S：One day, a duck fell into a hole. He cried for help. A monkey came. He tried to help the duck
with a pole, but that didn't help. An elephant came. He used his nose to reach the duck. But he failed.
A bear came. He had a good idea. They poured some water into the hole. At last, the duck got out.
They were happy.
