从A、B、C、D四个选项中，选出可以填入空白处的最佳选项。

21．We were shocked to hear the news that       two Chinese engineers were shot dead in Afghanistan. Worse still,         third one died in a truck bombing the next day.

       A．/, a                         B．the, the                   C．the, a                      D．/, the

22．— When         the next train leave for Boston, please?

    — Usually at 13:15, but because of a small accident on the line, it      at 13:45.

       A．does, is going to start                                  B．will, starts

       C．does, will start                                            D．will, is to start