21. Do you know how much time and effort they devoted________ such a complicated project?
A. to complete B. completed C. completing D. to completing
22. Words failed to ________ my feelings the moment I saw my long-lost sister.
A. control B. convey C. exchange D. affect
23. ---Do you know the timetable of the school bus?
---Sure, the first trip________ at 6:30 a.m. and usually continues until 4 p.m. on weekdays.
A. will start B. starts C. is starting D. started
