Which component remains common when making yellow-green and blue-green?

Correct answer: Yellow and blue

The governing concept is secondary-colour mixing. Green is produced by combining yellow and blue. Yellow-green contains more yellow, whereas blue-green contains more blue, but both mixtures still share yellow and blue as their basic components. Red and yellow would tend toward orange, and black and white would only change value, not create these green mixtures. Therefore, option B is correct.