To increase awareness of lung cancer caused by smoking, an NGO decided to post photos and tweets of ...

To increase awareness of lung cancer caused by smoking, an NGO decided to post photos and tweets of people suffering from the disease.
 
  Information on how lung cancer could be prevented was posted on a website, and anyone could visit and post comments. This changed the public's perception toward lung cancer and a lot of people started to volunteer to help the people suffering from the disease. Which factor of persuasion was used in this scenario?
   a) Audience participation
   b) Clarity of message
   c) Source credibility
   d) Appeal to self-interest