21．Jack left ___ message for me, saying he was in ___ trouble．
A．a; the B．a; 不填 C．不填; 不填 D．the;a
22．—What a boy! He could speak five languages at the age ten．
—He must have a ___ for language．
A．present B．try C．sense D．gift
23．My boss made __ clear that one in three of us will have to leave next month．
A．it B．us C．that D．this
