Explain why the lower respiratory tract is essentially sterile.

The lower respiratory tract is essentially sterile because epithelium lining is the respiratory tract that covers the bottom respiratory tract sterile. It basically prevented the mucus accumulation in lungs. The macrophages is the immune system part that can digest or inhaled any harmful substances.

the answer would be 3

you didn't give any options but heres what i can tell you: an inference is likely to change based on additional observations. the latter is something that you have seen or sensed using your sensory organs while the former is like a conclusion out from what you have observed.