Which adjustment should be made to make yellow-orange more reddish?

Correct answer: Increase orange or red influence

The governing concept is colour proportion in a tertiary mixture. Yellow-orange lies between yellow and orange, so increasing the orange or red influence moves its visual position toward red and makes it appear more reddish. Increasing yellow would push it toward yellow, while blue or green would introduce a different colour direction rather than a controlled red shift. Therefore, option B is correct.