The city zoo bought a new kangaroo    from Australia. It was famous for jumping very high. The zoo keeper was worried that the kangaroo would run away. He built special walls around it. But the next morning, people found that the animal was playing around outside. So the zoo keeper made the height of the walls 5 metres. But the kangaroo got out again the following day. The zoo keeper felt very angry, so he made the walls as high as lo metres, but the kangaroo still got out. "How high do you think he'll keep on building the walls?" a giraffe asked the kangaroo. "I don't know," said the kangaroo. "Maybe they'll reach 300 metres. It all depends on whether he remembers to lock the gate." What did the zoo keeper do to stop the kangaroo from going out?
To build the high walls. To lock the gate. To stay with the kangaroo. He didn't give the kangaroo food.