单选题 Vegetables are cheap ______ when they are in season.
A. buying B. to buy
C. to be bought D. to buy them

【正确答案】 B
【答案解析】[解析] 当不定式作表语(或宾补)形容词的状语，又与句中的主语(或宾语)有逻辑上的动宾关系时，虽然不定式有被动意义，但只能用主动形式。