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?

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2. Why wasn't Frank happy?

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3. Who came to see Frank one day?

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4. Why didn't Frank open the door?

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5. Did Frank hear the knock?

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