题目内容：

阅读短文从方框中选择适当的单词填空（每词限用一次）

by    mountains    if     finally   long

     Long long ago, there was a very old man called Yu Gong. There were two 1.           Near his house. They were so high and big that it took a2.       time to walk to the other side.The old man told his family that they should help him to move the mountains.

     Yu Gong and his family kept on digging day after day and year after year. 3.       ,a god was so moved 4.      Yu Gong that he sent two gods to take the mountains away.

    This story reminds us that you can never know what will happen 5.       you don't try to do it．