A doctor was delivering a presentation about the perils of using illegal intravenous drugs to a group of drug addicts at a rehabilitation center. He said consuming such drugs exponentially increases their risk of contracting hepatitis C
He also showed them gruesome pictures of people suffering from liver failure after contracting the disease, which ultimately led to their deaths. What persuasion technique was the doctor using in the presentation?

a. People respond to dissonance.
b. People respond to meet needs.
c. People respond to positive messages.
d. People respond to credible messages.