改为被动语态：1.He has worked out the problem.2.We have planted more than 100 young trees.3.We must keep our classroom clean an
问题描述：
改为被动语态：1.He has worked out the problem.2.We have planted more than 100 young trees.3.We must keep our classroom clean and tidy 4.My mother bought me a new sweater last Friday.
答
1.The problem has been worked out by him.2.More than 100 young trees have been planted by us 3.Our classroom must be kept clean and tidy 4.I was bought a new sweater by my mother last Friday.或是 A ne...