18. 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) superfical, as when the three major networks each
问题：
as when什么意思？开头的it指什么？谢谢大家指教！ | 
