Orbital speed is the speed with which a planet moves around the sun. The speed is determined by:

Question

a)the mass of the planet only
b) the mass of the sun only
c)both the mass of the planet and the mass of the sun
d)the mass of the planet and it's distance from the sun
e) the mass of both the planet and the sun and the distance between the two

I'd guess E, but I honestly don't know.

Answer 1

Your intuition is correct. The correct answer is E.
The orbital motion depends upon the SUM of the planet and sun's masses. The planet's mass is usually negligible compared to its sun.