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

(C)superficial if the three major networks all

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

答案是E. E选项后面的broadcast不用单数么，as when搭配合理么？

因为前面用了as much as 20% of the leaf and small stem material 说明了作者把leaf 和small stem material 看成一个不可数的整体

同意楼上的分析

as when搭配合理，其实是代表重复前面的一句话：

等于

Although if claims to delve into political issues, television can

be superficial；Although if claims to delve into political

issues, television can be superficial when ......

这样说很累赘，就用as代替

我们常常说的

as is know to you all, i am always hard working.

这个as 也是后面一整句话