After you have finished reading a book or a magazine in the reading-room, put it back ________ it used to be.

1. A.
   what
2. B.
   that
3. C.
   in which
4. D.
   where

After you have finished reading a book or a magazine in the reading-room, put it back ________ it used to be.

[　　]

After you have finished reading a book or a magazine in the reading-room, put it back ________ it used to be.

[　　]