Which colour mixture can be used to make a basic brown?

Correct answer: Red and green

The governing concept is complementary-colour mixing. Red and green lie opposite each other on the colour wheel, so their pigments partly neutralise one another and commonly produce a brown or muted earthy colour. Mix a small quantity of green into red gradually, because the exact result depends on pigment strength. Yellow and white make a light tint, blue and white make blue lighter, and red and white make pink. Therefore, option A is correct.