21．The moment we heard the news of the earthquake, we began to ________ the work to rescue those who were trapped in the building.
A．set off B．set down
C．set aside D．set about
22．I’m terribly sorry to turn you down this time, but I promise I will ________ to you next time.
A．pick it up B．make it up
C．turn it up D．set it up
23．—Hey, dear! Guess what? I’ve got a pay rise!
—This ________ a celebration! Let’s go to sing karaoke tonight.
A．calls for B．works out
C．brings about D．pays for
