Question

从句,疑问句后什么时候要加介词?

Answer 1

关键看动词和所修饰的词之间的意义关系

如：

I have two letters to write.(不用介词）

I have two pens to write with .(要用with,因为指的是 write with...pen)

I have no paper to write on ( 要用on ,指“写在纸上”）