Question

8. Apples are usually         ，and eggs are sometimes sold by the dozen. (sell)

苹果一般按重量销售，鸡蛋有时按打销售。

Answer 1

8. sold by weight by意为"根据，按照"，其后若为抽象名词时，名词前不加冠词；其后若是表计量单位的名词时,名词前加定冠词。