Keys _______ opening the lock in the door.

A. used for????????? ????????????? B. are used??????? ????????????? C. are used to?????? ????????????? D. are used for

Keys _______ opening the lock in the door.

A. used for???????? B. are used?????? ????????????? C. are used to???? ????????????? D. are used for

Keys ________ used for ________ the doors．

1. A.
   is; opening
2. B.
   is; opened
3. C.
   are; opening
4. D.
   are; opened

Keys are used by people ________ doors.

1. A.
   for open
2. B.
   for opening
3. C.
   with opening
4. D.
   to opening