What is not a function of mucus in the nasal cavity?
a) to moisten air entering the respiratory system
b) to trap particles entering the respiratory system
c) to break down oxygen entering the respiratory system
d) to warm air entering the respiratory system

D) to break down oxygen entering the respiratory system

Explanation:

Because the function of mucus in the nasal cavity is warm, moisturize and filter air entering

answer: proteins

explanation: complement is   system of circulate in the blood in a inactive form

i believe is what you're looking for?