Which one is a type of barrier

Chemical barrier

Sweat, tears, mucus, and saliva break down and destroy pathogens. There are chemicals in the body excretions that are breaking down pathogens.

i believe that the answer is c.

a. as the temperature increases, the kinetic energy of the gas molecules increases & the molecules move faster & further away from each other.

b. if you decrease the temperature of a fixed amount of gas at constant pressure, the combined gas law reduces to charles's law. in this case, volume will also decrease.