I saw a girl dance under the tree yesterday.变为被动语态
问题描述：
I saw a girl dance under the tree yesterday.变为被动语态
答
a girl was seen to dance under the tree yesterday
saw sb. do sth. 变被动态应为 be seen to do sth.
答
A girl was seen dance under the tree yesterday (by me).
括号中的可以省略。
答
A girl was seen dancing under the tree yesterday by me.
如有问题,欢迎继续追问：）