21．The video is too loud，could you ________，please?

A．turn up it             B．turn down it            C．turn it up                      D．turn it down

20．-- ________ have you been studying in your school?   --For two years．

A．How many           B．How often                  C．How long               D．How much

19．________ you speak German? ________ Yes．a little．

A．Can                     B．should                 C．May                      D．Must

18．He ________ his homework when I went to see him．

A．did                      B．was doing            C．is doing                 D．does

17．Tom，your brother is young．You ________ take care of him．

A．could                         B．will                     C．would                    D．should

16．He didn't tell me when he ________．I'll tell you if he ________．

A．will come；comes                                   B．will come；will come

C．comes；will come                                     D．comes；comes