读故事，将句子填写完整。
Today is Sunday. Bob goes to the zoo with his friends. He climbs up the wall to see the tigers and lions. A zookeeper shouts at him, "Don't do that. It's dangerous." He tries to touch the bear in the cage. A zookeeper shouts, "Don't touch it. It is dangerous." He wants to catch the ducks in the pool. A zookeeper shouts, "Stop! It's dangerous." Bob comes back home sadly. His mother asks him, "How's the zoo today?" Bob says, "It's no fun. Everything is dangerous!"
