21．Donny helped us get the tickets．We __________to Guangzhou next Wednesday．
A．flew B．fly C．are flying D．will have flown
22．My sister will get up early tomorrow morning，because the train to London _________at 6:00 a．m．
A．will leave B．is going to leave
C．leave D．leaves
23．He ________more than 5,000 English words when he entered the university at the age of l5．
A．had learned B．would have learned
C．learned D．has learned
