16、Is oxygen the only gas                      helps fire burn?

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

17、The Second World War                     millions of people were killed ended in 1945.

       A．on which        B．where             C．in that            D．during which

18、The train                     she was travelling was late.

       A．on that           B．for which C．on which        D．which

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

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

20、I’ll show you a store           you may buy all                you need.

       A．that, that              B．which, that            C．where, which         D．in which, /16、D                  17、D                  18、C                  19、C                  20、D