The exercise is not                  difficult but just needs care and patience.
A. by itself              B. of itself             C. in itself             D. for itself

The exercise is not difficult______ but just needs care and patience.
A. by itself  B. of itself  C. in itself  D. for itself

The exercise is not _____ difficult but just needs care and patience.

A. by itself　　 B. of itself　　 C. in itself　　 D. for itself