**Core Concept**
Combined Oral Contraceptive Pills (OCPs) contain both estrogen and progesterone, which modulate the hypothalamic-pituitary-ovarian axis to prevent ovulation, thicken cervical mucus, and alter endometrial lining, thereby preventing pregnancy. The benefits of combined OCPs include improved menstrual regularity, reduced menstrual cramps, and decreased risk of certain gynecologic conditions.

**Why the Correct Answer is Right**
The correct answer includes **b) PID** (Pelvic Inflammatory Disease) and **e) Ectopic pregnancy**. The progestin component of combined OCPs helps to reduce the risk of ectopic pregnancy by preventing the fertilized ovum from implanting outside the uterus. Additionally, combined OCPs have been shown to decrease the risk of PID by thickening cervical mucus, making it more difficult for bacteria to ascend into the upper genital tract. The progestin component also has anti-inflammatory properties, which may contribute to its protective effects against PID.

**Why Each Wrong Option is Incorrect**
* **Option A:** Hepatocellular adenoma is actually a risk associated with the use of combined OCPs, particularly those with high estrogen content. The estrogen component can stimulate the growth of liver cells, increasing the risk of adenoma formation.
* **Option C:** Ovarian cysts are not directly prevented by combined OCPs. In fact, the estrogen component may actually increase the risk of ovarian cysts, particularly polycystic ovary syndrome (PCOS).
* **Option D:** Fibrocystic disease of the breast is not prevented by combined OCPs. The estrogen component may actually worsen breast fibrocystic changes.

**Clinical Pearl / High-Yield Fact**
Combined OCPs can also have a beneficial effect on acne by reducing androgen production and improving skin clarity. This is particularly useful for women with acne who are also at risk of pregnancy.

**Correct Answer:** B. PID and Ectopic pregnancy.