When asked to explain ________ he does to make his students so fascinated with his lessons, the teacher paused and thought deeply.

  A. what it is that                                                B. that what it is                      

C. what is it that                                         D. that what is that

When asked to explain ________ he does to make his students so fascinated with his lessons, the teacher paused and thought deeply.

  A. what it is that                                    B. that what it is                 

C. what is it that                             D. that what is that

 When asked to explain _____ he does to make his students so fascinated with his lessons, the teacher paused and thought deeply.  

A. what it is that            B. that what it is           C. what is it that           D. that what is that