Well, this question is tricky
D: it definitely isn't D since the more sex with different people you have the greater chance you have of contracting stuff.
C: if you stop your self from sex completely you have a 100% chance of not getting a STD.
B: if you only have sex with one person then that cuts down on the chance of std, unless that one person has an std
A: vaccination, seems like the best option if there is indeed a option to vaccinate or check for disease
I am guessing A: Vaccination
It is either that or c
I hope this helped
