21. --- Do you really mean to prepare our lecture two months in advance?
--- Sure. Anyway, ___________
A. a good beginning is half done. B. a bird in the hand is worth two in the bush.
C. a fall into a pit, a gain in your wit. D. the early bird catches the worm.
答案D。 The early bird catches the worm. “早起的鸟有虫吃”；符合语境。A项意为“良好的开端是成功的一半。”；B项意为“二鸟在林，不如一鸟在手； 多得不如现得”；C项意为“吃一堑，长一智”。
