His English, ______ used to be very poor, is now excellent.
A. that        B. which         C. it                D. whom

His English, ______ used to be very poor, is now excellent.

A. that　　　 B. which　　　　 C. it　　　　　　　 D. whom

His English, ______ used to be very poor is now excellent.

A. which   B. that    C. it    D. whom