Question

As we all know, apples are sold by ________ weight, and socks are sold by ________ dozen．

1. A.
   the; a
2. B.
   /; a
3. C.
   /; the
4. D.
   the; the

Answer 1

C
by time, by weight, by height这些时间、重量、高度，意思很广的词无冠词；by the hour, by the kilogram, by the meter这些时、公斤、米，是time, weight, height的具体化就有冠词the; by the dozen是固定短语“大量，很多”。故本题选择C项。