Answer:
Physical barrier
Explanation:
Innate immunity is our first line of defense against invading organisms . inmates immunity include physical barriers, antimicrobial substances, normal flora etc.
The skin and mucosa of stomach and of other organs serve as first line of defense and the function of defense is both mechanical and chemical. The mechanical function involves physical barrier that prevent entry or translocation of organisms. The chemical function include substances that inhibit growth or destroy microbes e.g. gastric acid in the stomach.
It is still flat but the city air and gas may be more perception
