pp2-1-13 help

cotton is grown throughout the world, and ---year about 50 million bales, weighing hearly 500 pounds a piecem are produced.

A, each B, a C, by a, D in which

confused A and B, please explain to me, thanks.

我选A，虽然A也可以有EACH的含义，但EACH还是在强调“每一年”，是个连续的概念，A强调在单个一年。

另外个人感觉结构和改错都考的是正式文法，A应该更口语化些。有更严格的选项就尽量选更严格的。