8. Apples are usually sold by ____ weight, and eggs are sometimes sold by ____ dozen.
   A. the; the      B. /; a           C. /; the             D. the; a
8. C。by weight “按重量计算”；介词by表示计量时, 其后表示“时间、长度、体积、面积”的名词前要加定冠词。by the dozen“按打计算”。再如by the piece/pound/yard按件/论磅/按码。