If pink becomes too light what should be added to make it deeper?

Correct answer: A little red

The governing concept is strengthening the base hue in a tint. Pink is commonly understood as red lightened with white, so adding a small amount of red increases the red pigment and makes the pink deeper and more saturated. Option B is correct. More white would make the pink still lighter. Yellow would shift it toward a warmer peach or coral direction, while green is complementary to red and could dull or neutralise the mixture. The red should be added gradually to prevent the colour from becoming too strong.