Loudness and pitch _____, while intensity and frequency are _____.

A. vary according to the individual; are constant for all states of matter
B. are scientific measurements; objective
C. are subjective; scientific measurements
D. are properties of sound; properties of waves

I think it's C, but, again, I'd like another opinion.

you are right, the answer should be C.

It Should be D because the Loudness and Pitch are the properties of sound of course, and the Intensity and Frequency would be for waves.