The foot-in-the-door method is basically a psychological method where you ask for a small request first, then a bigger one later. So I think it's A, just because the others don't work. B is just straight up asking for a big favor, C is providing you with the "must-do" effect, and D is simply a favor for a favor.
3 is your answer hope this helps
Do you have options
that would help me out a lot
