Parental smoking is a possible confounding variable because: a. Mothers who smoke (or who are exposed to cigarette smoke) are exposed to more heavy metals over the course of their pregnancy.
b. Cadmium exposure can happen in the general population by eating foods that are grown in contaminated soil.
c. Women who smoke might not know they are pregnant. and A. Children who are exposed to cigarette smoke during infancy may experience lung damage and be more likely to develop asthma.
d. Asthma can develop at any point in a person's lifetime.
e. Laws in the US prevent the marketing and sale of cigarettes to children.