Examples of natural barriers include (mark all that apply):

The natural barriers include biochemical, physical, and mechanical, as well as inflammation of the body.

Natural barriers and the immune system defend the body against the species that leads to infection. The natural barriers include the mucous membranes, skin, earwax, tears, stomach acid, and mucus. Also, the usual flow of urine washes out the microbes, which enter the urinary tract.

answer: ice crystals in air

the water from the water body or another source of water gets evaporated as water vapor as an effect of heat on water. these water vapor rises in the upper layers of the earth atmosphere under high atmospheric pressure. the atmospheric pressure of these water molecules starts to decrease due to the effect of cold air. the invisible water vapor condenses into visible water droplets and ice crystals.these ice crystals and water droplets being less denser than the surrounding air floats on air as clouds.