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 doubt whether I can be admitted to my dream university in two months.
-- ______. Everything is possible.
A. Don't mention it B. Never give up C. Behave yourself D. It depends
22. -- What do you think of the set of popular science books?
-- It couldn't be better! It ______ many problems we are interested in exploring.
A. covers B. consults C. measures D. writes
23. -- Are we going sightseeing sometime next month?
