4) all of the following are sources of air pollution, except
a. chlorofluorocarbons (cfcs).
b. heavy metals such as mercury.
c. nitrogen oxides from automotive exhaust.
d. small particles of smoke and dust in smog.

With the choices given, the answer to the biology question presented above would be b. heavy metals such as mercury. Heavy metals contribute to soil pollution more than air pollution. The other choices are sources of air pollution. Thus, letter b is the answer.

the glands which are associated with each description is given below:

pancreas - is an endocrine and exocrine gland that secretes juices with enzymes for digestion. salivary glands- with protection and digestion in the mouth. liver- secretes bile for digestion.   lachrymal glands - secrete tears to moisten eyes and protect them from particles and infection.   sweat gland -regulates water, salt, and temperature. oil glands - to form a protective barrier on the skin.   goblet cells - secrete mucus for protection.