I find these problems are easy ____

题目

I find these problems are easy ____
a.to be worked out b.to work them out
c.to work out d.to be worked them out
选C 表是被动为什么不选A呢?

答案

具体原因我也说不清,但有很多这样的例子：
the book is easy to read
the movie is good to watch
the job is fun to do
your voice is nice to hear