What Incentive Does a Presidential Candidate Have to Debate His

What incentive does a presidential candidate have to debate his or her opponent?

A) Engaging in debate generally leads to an increase in favorability for both candidates.
B) Debates have become expected of candidates, so not debating would break tradition.
C) The Constitution requires that presidential candidates debate one another publicly.
D) Refusing to debate might cause voters to view that candidate as weak and timid.