从A、B、C、D四个选项中，选出最佳选项，并在答题卡上将该项涂黑。
例：It is generally considered unwise to give a child______he or she wants.
A. however B. whatever C. whichever D. whenever
答案选B.
21. The first edition_______in 1955 and_______a best seller ever since.
A. was published; had been B. had been published; had been
C. has been published; has been D. was published; has been
