Helping a social movement is, usually, something related to making it known and having people to create empathy with the cause. That's not succeeded by secrecy, so we can ignore answer A and also B, that deals with governmental control over the content of the social movement. D is also talking about being secretive, which is also contrary to helping the movement, which leaves us with C.
C - people are able to share snapshots of their experiences.
That way, the social movement can gain more followers and people can empathize with it.