The question is incomplete. The complete question is :
A platypus foraging for prey can detect an electric field as small as 0.002 N/C.
-To give an idea of sensitivity of the platypus's electric sense, how far from a +80nC point charge does the field have this magnitude?
Solution :
Given electric field, E = 0.002 N/C
Charge, Q = + 80 nC

or 

R = 600 m
This is the distance of the charge from the point of observations.
F=mg
if m doubled, F would double as well
Answer:
According to your question although I think an object undergoing uniform circular motion is moving with a constant speed. Nevertheless, it is accelerating due to its change in direction. The direction of the acceleration is inwards,therefore a force perpendicular to an objects velocity change the direction of the velocity but not its magnitude.
Imma guess A! Idk if it’s 100% correct tho so I’d check that!