-------______ either you or he going to visit the exhibition? 

 -------He is. I can't _______ working until 6 o'clock.

      A．Is; knock off                                              B．Are; knock away

      C．Are; knock off                                           D．Is; knock away

―       either you or he going to visit the exhibition?

―He is. I can’t       working until 6 o’clock.

       A．Is; knock off                                       B．Are; knock off

       C．Are; knock away                                 D．Is; knock away