In which situation will green be considered cool?

Correct answer: When it contains more blue

The governing concept is relative colour temperature. Green can lean toward yellow-green, which appears warmer, or toward blue-green, which appears cooler. Adding or increasing blue shifts green toward blue-green, so option D is correct. More yellow generally warms the colour, while red also pushes it toward a warmer direction. Merely placing it beside orange may create comparison, but it is not the clearest colour-making condition here.