问题
I found his theory difficult________.[ ]
A: understand
B:to understand
C: understood
D:to be understood
B:to understand
C: understood
D:to be understood
正确答案是：
同类题型
She wrote a month ago, ______ we’ve heard nothing.
Not until ___ on TV ___ that theChinese was rescued by the European Union Task Force.
Once harm ______ to the environment, it takes years to have the system recovered
23. Your room is terribly dirty; you get it cleaned in two hours, or Mum will be angry.