Which pair should be used to create red-orange?

Correct answer: Red and orange

The governing rule is that a tertiary colour is formed by mixing a primary colour with the neighbouring secondary colour on the wheel. Red-orange is therefore made from red and orange, so option B is correct. Red and green are complementary, and yellow-violet are also complementary pairs that tend to neutralise or dull one another. Blue and orange are another complementary pair, not the required adjacent pair.