Which mixture may be suitable for producing olive green?

Correct answer: Add a little yellow and very little black to green

Olive green is a subdued, yellow-leaning green. The governing mixing idea is to modify an existing green with a small amount of yellow and then reduce its brightness slightly with a tiny amount of black. Therefore option D is suitable. Red and white make pink, blue and white make a light blue tint, and violet and white make a light violet tint, not olive green.