I never thought about this when I went through this question, but this is a good point.
The q-stem asks specifically regarding the nucleophilicity of this compound. Amine, which are presented in this case, are usually excellent nucleophiles because of the lone pairs. Remember that nucleophile strength is decreased if it is sterically hindered, not allowing the electrons to attack the electrophile. This leaves you with C and D. C is correct in nature, but ask yourself the question backwards. Is H+-sponge a bad nucleophile because it's aromaticity? We can compare the benzene ring (aromatic) with a cyclohexadiene. The cyclohexadiene (not aromatic) will probably still make the molecule a bad nucleophile, because its so sterically hindered. (Though, I think they wanted you to look more into the 4 methyl groups.) Another point is, the benzene ring is an EDG (activating) so it actually contributes to nitrogen being a good nucleophile in a way...
You then ask yourself, do sterically hindered molecules usually make molecules bad nucleophiles? Yeah, they do! ->>>D
That is correct, I think I just meant to say that the benzene ring is not the reason why it could be a good or bad nucleophile in this case. Compared to other EDG groups, benzene would be a weaker activator compared to like methyl or something.