One out of six teenagers who are sexually active gets pregnant.
As teens, we would all know it, if we were to have sexual relation constantly either with a condom or without one, either the condom would rip, or possibly you may not even put a condom on in the first place. And this would be able to resolve in 'pregnancy'. We can't say that you would break up with your boyfriend, because that does not always happen. And we can't say that you would have a violent relation, because that could not always happen as well. And that would be why B would make more sense of an answer.
