Sound is a type of wave.
a. water
b. surface
c. mechanical
d. electromagnetic

Sound is an example of a mechanical wave. Mechanical waves are the kinds of waves that cannot be propagated without a medium. As such, these waves cannot travel through a vacuum, just like how sound cannot travel through space, since space is a vacuum.

I would say the answer is B. That's what makes the most sense to me but I'm not certain.