A compound consists of only magnesium, carbon, and oxygen..need help!

I feel like this question should be easy but I'm not getting it? I was going to choose D.

A compound consists of only magnesium, carbon, and oxygen. If the percentage by mass of Mg is 28.8% and that of C is 14.2%, what is the percentage of O?
A. 43.0%
B. 22.5%
C. 16.0%
D. None of the other choices is correct
E. 47.0%

The only thing I can think of is MgCO3 ... which has a molar mass of 84.3139

taking (3*15.9994) / 84.3139 = .569 or 56.9 % which is none of the above.

I'd go with D.

None are correct. The answer is 57%.