问题描述：
1.A friend is now repairing the piano in the workshop.
2.They are building a new bridge over the river.3.The postman delivered a newspaper this morning.4.My mother gave me a present yesterday.5.The police have arrested the thief.6.He was typing a letter 改被动语态
2.They are building a new bridge over the river.3.The postman delivered a newspaper this morning.4.My mother gave me a present yesterday.5.The police have arrested the thief.6.He was typing a letter 改被动语态
问题解答：
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