请教一道大全题目

大全SEC-12

请问这道题为什么选E，as when是什么用法，加了each是否动词还用复数，C为什么不对，谢谢

19.   Although it claims to delve into political issues, television can be superficial such as when each of the three major networks broadcast exactly the same statement from a political candidate.

(A) superficial such as when each of the three major networks

(B) superficial, as can sometimes occur if all of the three major networks

(C) superficial if the three major networks all

(D) superficial whenever each of the three major networks（E）

(E) superficial, as when the three major networks each

 as when,连词+副词,就象....当...时候

 主语(复数)each+谓语(复数)

 if表示条件,如果...感觉放在这里意思不对,另外all强调整体,不如each表达的好