Which group is most useful for creating a warm colour sequence in a sunset?

Correct answer: Red, red-orange, orange, and yellow-orange

The governing concept is warm colour harmony and gradual progression around the warm side of the colour wheel. Red, red-orange, orange, and yellow-orange are visually warm and can be arranged in a smooth sequence from deeper red toward brighter yellow-orange, which suits the glowing appearance of a sunset. Therefore, option A is correct. The other groups are mainly cool or mixed hues, so they would not create the same warm sunset progression.