Center of mass of the solar system?

On a recent test my teacher asked this question: The center of mass of the solar syster is a) at the center of the sun b) varies as the planets rotate c) outside the sun d) none of the above I put down that it is choice (b) because as the planets move they would change the weight distribution and would... show more On a recent test my teacher asked this question:
The center of mass of the solar syster is
a) at the center of the sun
b) varies as the planets rotate
c) outside the sun
d) none of the above

I put down that it is choice (b) because as the planets move they would change the weight distribution and would change the center of gravity.
He marked me wrong saying that the right answer is (c) which is true, but so is my answer
Any ideas on how i can debate with him to get the points?
thanks
Update: in the text book it says that the center of the universe is outside the sun which i agree with because of the size of the planets

Does anyone know of and guess to how much any of the planets weigh?
Update 2: yea im going to have to agree that as the planets move around they change the center og gravity, also because they all have different orbits and sometimes become closer and farther away, changing the weight
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