The trap in this question is getting caught up in the linking words after superficial: such as, as, if, whenever, or as when. If we notice that there's a verb just outside the underlined portion ("broadcast"), we can use that to narrow down our answer choices.

In A, the subject for "broadcast" is "each of the three major networks." "Each" is singular, while "broadcast" is plural, so we have an agreement error.

In B, the subject is "all of the three major networks," which works. However, it changes the meaning of the original. In A, we knew television was superficial WHEN this event happened, which is fairly definite. B uses "if" instead of "when," which makes it conditional

In C, the subject is "three major networks," which works. However, it uses "if" instead of "when," so we can eliminate it as we did B.

D uses the same subject as A, so we can eliminate it.

E uses the same subject as C, so agreement is fine. It also keeps "when" instead of "if," so it preserves the original meaning.