Personally, I agree with your answer, namely that the likely-intended event happening here is one of acceleration. Having said that, I also want to add: it pains me to see this type of wording because, clearly, it is vague and only invites confusion of the type you are talking about.
Good luck!
the answer would be B. the back emf increases, and the current drawn from the socket increases
more current is needed to make the motor move, like when you try to self crank a motor and the back wires are touching its harder to crank. and the emf increases since more current is being drawn in, strengthening the emf or increasing the emf
The frequency of sound waves goes up, so the pitch goes up as well. More frequent=higher pitched
