As is known to all , theory is based on practice and ______ serves practice.

1. A.
   by chance
2. B.
   by turn
3. C.
   in return
4. D.
   in turn

As is known to all , theory is based on practice and _______ serves practice.

    A. by chance       B. by turn    C. in return       D. in turn

 As is known to all , theory is based on practice and _______ serves practice.

    A. by chance       B. by turn    C. in return       D. in turn

As is known to all , theory is based on practice and _______ serves practice.

As is known to us all, theory is based on practice and __________ serves practice.

A. by chance　　    　　   B. in turn 　　　　　　　　　　 C. in return　　　　 　　   D. by turn