The answer is C. Mountains. I hope this helped!
I'm going to quote something that might help you...
"The Doppler effect is the apparent change in the frequency of a wave motion when there is relative motion between the source of the waves and the observer. Well known examples include the change in pitch of an ambulance or police siren, as it approaches and then recedes from you, or the same effect from a passing train."
This is not mine I am simply quoting something that might help you.
Answer:
Explanation:
As we know that mass is the product of volume and density
so we will have
here we have
so we will have
so we will have
now let the position of Pluto is at origin so we have