When a contest between two candidates is very close, people are
a. more likely to vote.
b. less likely to vote.
c. unlikely to notice.`
d. more likely to join a political party.

When a contest between two candidates is very close, people are less likely to vote and in return, the candidate with a lesser support and is expected not to win may win instead. Because people will be expecting that the two contending and strong candidates will win anyway because many people are expected to vote them. So other people will choose to vote the lesser candidate, trying to even the probability of the strong winning streaks of the other candidates.

Velocity is the speed of an object in a certain direction so you'd need to know speed and direction