Fluctuations in estrogen are common in women of reproductive age. what side effect do you think may occur in post-menopausal women who take estrogen supplements?
a. breast cancer
b. high blood pressure
c. diarrhea

(a). Breast cancer.

Explanation:

HRT or hormone replacement therapy can be defined as a type of hormone therapy, which is used for the treatment of menopause symptoms in females. It includes various hormones, including estrogen.

Estrogen is a female hormone that is normally synthesized in females during their reproductive age, which helps in regulation of menstrual cycle, production of milk, and thickening of uterus lining.

However, increased level of estrogen also increases risk of developing certain types of cancers, such as breast cancer as it makes the cells to multiply rapidly and increase production of mutant cancerous cells (if present).  

Hence, a woman who is taking estrogen as HRT can develop breast cancer due to higher level of estrogen. Thus, the correct answer is option (a).