阅读理解。

　　One day the workers of a zoo called a meeting to discuss a problem．The kangaroos(袋鼠)were running out of their cage(笼子)．The workers decided that the cage was too low so they raised it from one meter to two meters．However, the next day the kangaroos were outside of their cage again．So they raised the cage a second time．

　　The next morning, to their surprise, the kangaroos were again loose(自由的)．They decided to raise the cage to a height of 10 meters．

　　Later a giraffe(长颈鹿), talking with some kangaroos, asked them,“Do you think they will go on raising your cage?”

　　“Hard to say,”said one kangaroo．“It all depends on whether they continue to forget to fasten(固定)the cage door．”