One day the staff members of a zoo called a meeting to discuss the problem--how to deal with the kangaroos that were found out of the cage. They came to the conclusion that the cage was placed too low and decided¹ to raise it from one to two meters high. But the next day the kangaroos were still at large（详尽的，未被捕的） and they again raised the cage to three meters.

Quite beyond their expectation the next morning they saw the kangaroos still free to go about（着手做，四处走动） . They were alarmed and determined² to go to all the length by raising the cage to the height of ten meters.

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

"Hard to say," said a kangaroo, "if they continue forgetting to fasten the cage door."