21. According to _______ announcement by Guangzhou Price Bureau, _______ the new measures which have been taken recently are expected to cut the operation costs of each taxi driver by 1280 yuan.

      A. the; /                      B. an; the                    C. /; the                       D. an; /

22. It was four o’clock in the afternoon _______ they got to the station.

      A. that                        B. since                      C. when                     D. until