What is the correct way to make a warm red relatively cooler?

Correct answer: Add a slight violet or blue bias

Colour temperature is changed by shifting the hue bias toward a warmer or cooler neighbour on the colour wheel. A warm red can be made relatively cooler by adding a small amount of blue or violet, which moves it away from orange and toward the cool side. Therefore option B is correct. Orange and yellow make red warmer, while white changes value and may reduce intensity without reliably changing temperature; hence A, C, and D are incorrect.