Check, one by one, whether each element can ever be forced into a positive oxidation state.
Option A, oxygen: normally oxygen is minus 2, but when it bonds with the even more electronegative fluorine, as in OF2, it is oxygen that gets pushed to a positive plus 2 state. So oxygen is not the answer, it does show a positive state in that special case.
Option B, chlorine: chlorine forms a whole family of oxoacids, hypochlorous acid, chlorous acid, chloric acid and perchloric acid, where its oxidation state runs from plus 1 right up to plus 7. So chlorine clearly does take positive states.
Option C, fluorine: fluorine sits at the top of the electronegativity scale, nothing in the periodic table can pull electrons away from it. In HF, NaF, or any other compound, fluorine is always minus 1 or 0, never positive. There is no known compound where fluorine shows a positive oxidation number.
Option D, carbon: carbon is only moderately electronegative, so depending on the partner atom it can be negative (bonded to hydrogen, as in CH4, carbon is minus 4) or positive (bonded to oxygen, as in CO2, carbon is plus 4). So carbon is not restricted to negative states either.
Only fluorine has zero exceptions, so option C is correct.