The answer is D: discourages.
noun Deterrence: the action or the fact of deterring (preventing, stopping) people from doing something.
adjective Deterrent: Making someone less likely to do something by making it difficult for them to do it or by making them realize that it will have bad results.
A: encourage is the opposite of discourage.
B: increase: grow, expand, become greater.
C: label: classify, decribe, identify.