If red is increased in yellow-orange which tertiary colour may the mixture approach?

Correct answer: Red-orange

The governing concept is directional colour mixing. Yellow-orange contains yellow and orange; increasing red strengthens the red side of the orange component. As the mixture moves away from yellow and toward red, it approaches red-orange, so option B is correct. Blue-violet and blue-green introduce blue influences, while yellow-green shifts toward green; none follows the stated increase in red.