阅读理解。 Frank bought a new doorbell, but nobody seemed to notice it. When his friends came, they knocked heavily at the door. Frank was not happy about it. One day a friend came to see Frank. He knocked at the door loudly. Frank came to the door, but didn't open it. He shouted at the visitor from inside.' I can't hear you! Please ring the doorbell!' 根据短文内容,回答下列问题: 1. What did Frank buy? ______________________________________________________________ 2. Why wasn't Frank happy? ______________________________________________________________ 3. Who came to see Frank one day? ______________________________________________________________ 4. Why didn't Frank open the door? ______________________________________________________________ 5. Did Frank hear the knock? ______________________________________________________________