Answer choice B is Correct.

Choices C and D are eliminated because the N-terminal is deprotonated (uncharged) in organic solvent while the C-terminal is protonated (uncharged) in organic solvent. Choice A can be eliminated because a protic solvent would be reactive, not inert. A protic solvent (such as ethanol) can attack acetic anhydride and undergo a substitution of the carbonyl.