As rule, apples are sold by weight and eggs by dozen.
A. a; 不填；the
B. a; the; the
C. a; a; the
D. the; 不填；不填
网友回答
(答案→)A. a; 不填；the
B. a; the; the
C. a; a; the
D. the; 不填；不填
解析：as a rule(通常地)是固定词组；在度量名词前，表示付工资、卖、租等方式时，用the, 如paid by the hour (day, moth, piece…), sold by the yard (dozen, ton…)，比较by weight (按重量)。