用被动语态改写下列句子
问题描述：
用被动语态改写下列句子
People usually post Christmas cards in December
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People use computer to search for information
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Cleaners collect rubbish every morning
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Peter finished my science project ono time
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Someone invited Linda to a birthday party
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I heard Amy singing in the next room just now
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答
Christmas cards are usually posted in December (by people).Computers are used to search for information (by people).Rubish is collected by cleaners every day.My science project was finished on time by...