If a student mixes red and yellow to make orange, what property of primary colours does this demonstrate?

Correct answer: They combine to form secondary colours

The governing concept is subtractive pigment mixing in the traditional RYB system. When two primary pigments are combined, a new secondary colour can result: red plus yellow produces orange. Thus option C correctly describes the demonstrated property. Option A is too limited, option B contradicts the definition of primary colours, and option D is not the normal result of this pair.