－Look! The telephone is broken. Someone damaged it ________ purpose.
－That may be right. But perhaps it was broken _________ accident.

—Look! The telephone is broken. Someone damaged it       purpose.

—That may be right. But perhaps it was broken       accident.

---Look! The telephone is broken. Someone damaged it ________ purpose.

---That may be right. But perhaps it was broken _________ accident.

－Look! The telephone is broken. Someone damaged it ________ purpose.

－That may be right. But perhaps it was broken _________ accident.

A．on;by            B．by;by             C．on;on            D．by;on

—Look! The telephone is broken. Someone damaged it       purpose.
—That may be right. But perhaps it was broken       accident

1. A.
   on; by
2. B.
   by; by
3. C.
   on; on
4. D.
   by; on