Why is snot green?

Why is snot green?
A - the colour comes from iron-containing enzymes in leucocytes that break down bacteria
B - it is the natural colour created when airborne particles react with the moist nasal passage walls and hair follicles
C - the colour is conferred by a specific gene designed to give snot a repulsive colour so that you won't eat it
(I think the answer is A)


