21. What ________great fun it is to have a swim on a hot day in summer!
A. a B. the C. an D. \
22. The number of people invited ______fifty, but a number of them ______absent for different reasons.
A. were; was B. was; was C. was; were D were; were
23. —Do you know the most ancient city in China—Xi’an well?
—No，this is the first time I ________ here.
A. came B. have come C. am coming D. come
