Only when class began ______that he had left his book at home．

Only when class began ______that he had left his book at home．

Only when class began ______that he had left his book at home．

A. will he realize    B. he did realize    C. did he realize    D. had he realized 

Only when class began ______that he had left his book at home．

1. A.
   will he realize
2. B.
   he did realize
3. C.
   did he realize
4. D.
   had he realized

. Only when class began ______that he had left his book at home．

A. will he realize    B. he did realize    C. did he realize     D. had he realized