Sir, it would be great if you share your reasoning as well.

I don't know something wrong with this question
so it is already hidden movement ok, so once it ------ mass media
reported can work
contradict can work
but mass media promulgate for such bad movement , I believe this answer make no sense

So the idea is that loyal followers left the movement BECAUSE the underground message(a bad thing) was circulated by the mass media.

aha so the message was the bad thing not the movement

"message of the underground, counterculture youth movement"

Why would the loyalists defect their ideology if the message is promulgated and publicized?

Does the message have a negative connotation? How would we know about it? Where are the clues?

why not reported, that would force people to leave the group?

-- Oh that's entirely incorrect.
1. C is "Not logical" or "logically sound"
2. Mass Media is a TOOL. Definitionally, it's a collection of reporting systems. Media reporters are different.
3. Mass Media is meant to be unbiased and it is only meant to report. It's a noun that is meant to carry neutrality.

4. CLUES "An underground group" "counterculture messages"...
These are people whose beliefs can cross the line of what is "socially acceptable".

5. You also have to understand the phrase "underground + noun". Underground market. Underground organization.
They are not on the "up and up"
Secret organizations. Resistance groups.
Historically, kept their involvement in these groups a secret.

Promulgate makes perfect sense, and to "defect" is the resulting verb.