从A、 B、C、D四个选项中，选出可以填入空白处的最佳选项。
21．I was told that ____ 10:15 flight would take us to Shanghai in time to reach _____ Fudan University．
A．/;the B．the; a C．a; the D．the; /
22．Thank you for the great trouble you to find us the right person for the job．
A．had B．got C．took D．made
23．The project alongside with the experiment we had once devoted so much time__________ perfectly．
A．to work out B．to working out C．to worked out D．has worked out
24．—Where is Bob? I cannot find him anywhere．
—He have been off long．I heard him make a call just now．
