Answer:
B
Step-by-step explanation:
The mass media influenced him, as his decision was directly caused by the show he watched.
It isn't his social environement, as this is where multiple people within his social groups already have this opinion, and this influences him.
It isn't interest groups because there is no indication of him being involved in this cause before.
It isn't his opinions because he did not come up with the idea himself, this view was inflicted on him by the show he watched.