What roles does mucus have in the immune system? O It traps germs so they do not get into the body.
O It helps people build immunity to diseases.
O It builds up defenses and antibodies against a disease.
O It makes antibodies to help humans fight disease.

It traps germs so they do not get into the body

People who utilizes the progression principle will ensure their exercise program increases in frequency, intensity, time, and type. the changes need to happen gradually in order to ensure they make gains in their fitness program. a person who doesn't utilize the progression principle can still gain health benefits from exercising, but will not continue to improve in cardiovascular fitness.