It was not until the teacher had explained it three times _______ how to work out the problem.

A. did he understand                                                        B. had he understood       

C. that he understood                                                      D. that he didn’t understood

—Does he know how to work out the problem ?

    —Yes , he has         a good idea to solve it .

   A. caught up with       B．kept up with       C．come up with      D．put up with

—Does he know how to work out the problem?
—Yes, he has _______ a good idea to solve it.

—Does he know how to work out the problem?---Yes, he has ___ a good idea to solve it.     ----Yes, he has ___ a good idea to solve it.

       A.caught up with   B.kept up with   C.come up with   D.put up with

     how to work out the difficult physics problem ,he asked the teacher for help .

A. Not to know   B. Not knowing  C. Knowing not    D. Not known