The answer should be B if i'm not mistaken. The sp2 hybridized nitrogen is going to be more basic because it is in a position to donate it's lone pair and pick up an electrophile, the lone pair is perpendicular to the π system, making it less likely to donate into making the ring aromatic. The sp3 hybridized nitrogen is in a position to donate it's pair into making the imidazole ring aromatic, and thus will do so, and its lone pair will not be available to an electrophile.