③.Apple are usually sold by ____weight and eggs are sometimes sold by ______dozen.

题目

③.Apple are usually sold by ____weight and eggs are sometimes sold by ______dozen.
A.the;the B./;a
C./;the D.the;a
请说明答案和选题原因,谢谢.
另外,问问dozen是一打,一打是几个啊?

答案

C.by weight
by the dozen ,这是固定用法
这个只有在作题的过程中积累
1打是12个