14. A cohort study is conducted to assess the relationship between oral contraceptive use and breast cancer. The study shows that in women with a family history of breast cancer, oral contraceptive use increases the risk of breast cancer with a relative risk (RR) of 2.10 and p value of 0.04. In women without a family history, no effect is observed (RR = 1.05, p = 0.40). The phenomenon described is an example of which of the following:
A) Confounding
B) Selection bias
C) Latent period
D) Effect modification