1.It's a very useful book.（用what改为感叹句）
问题描述：
1.It's a very useful book.（用what改为感叹句）
2.This is our teacher's office.(改为一般疑问句）
3.The car hit the tree yesterday.(改为否定句）
4.Mr.Brown said ,"Don't run across the street again,Mary."(改为间接引语）
答
what a useful book is !
Is this our teacher's office?
The car didn't hit the tree yesterday.
Mr.Brown said (that) not to talk in class.