Winter is the time of year ________ the days are short and nights are long.

[　　]

Winter is the time of the year      the days are short and nights are long．

    A．on which     B．that            C．when         D．where

Winter is the time of the year     the days are short and nights are long．

1. A.
   on which
2. B.
   that
3. C.
   when
4. D.
   where