Use the Following Information for Questions

Multiple Choice

Use the following information for questions:
Research is done to see whether taking oral contraceptives increases women's blood pressures. The blood pressures of women who take oral contraceptives are compared to the blood pressures of women who do not take oral contraceptive. A complicating factor is that the women who take oral contraceptives tend to be younger than the others. This must be taken into account because blood pressure increases with age.
-Which variable is a confounding variable in this study?

A) Age
B) Blood pressure
C) Oral contraceptive use
D) There are no confounding variables in this study.