As we all know, he has regretted wasting the precious time when he         studied hard playing computer games at school.

       A．should have     B．would have      C．might have       D．must have

As we all know,he has regretted wasting the precious time  he should have studied hard playing computer games at school．

A．where    B．that    C．on which    D．when

As we all know, he has regretted wasting the precious time______ he should have studied hard  

playing computer games at school.

As we all know, he has regretted wasting the precious time______ he should have studied hard   playing computer games at school.

1. A.
   where
2. B.
   that
3. C.
   on which
4. D.
   when

As we all know, he has regretted wasting the precious time______ he should have studied hard  

   playing computer games at school.

A. where        B. that                              C. on which       D. when