If a box is labelled primary colour, which colour may be inside it?

Correct answer: Red

A colour labelled primary in the traditional school-art model may be red, yellow or blue. Among the given choices, only red belongs to that group, so option C is correct. Green, orange and violet are generally secondary colours made by mixing pairs of primary colours: blue with yellow, red with yellow, and red with blue respectively. The label therefore rules out the other choices.