## Core Concept
The core concept here revolves around the selection of an appropriate Oral Contraceptive Pill (OCP) for lactating mothers. The primary concern is to choose a contraceptive method that does not adversely affect milk production or infant growth and development.

## Why the Correct Answer is Right
The correct answer, **Levonorgestrel-only pill (or progestin-only pill)**, is preferred for lactating mothers. This is because progestins have less effect on milk supply compared to combined estrogen-progestin pills. Estrogen can decrease milk production, so progestin-only pills are safer for breastfeeding mothers. Additionally, progestins are less likely to affect the infant's growth and development.

## Why Each Wrong Option is Incorrect
- **Option A:** Combined OCPs contain both estrogen and progestin. Estrogen can reduce milk supply, making them less ideal for lactating mothers.
- **Option B:** Although not specified, if this option implies another type of contraceptive, it's essential to understand that not all contraceptives are suitable for breastfeeding mothers, especially those that can interfere with milk production or infant health.
- **Option D:** If this option suggests a different type of hormonal contraceptive that includes estrogen, it would be incorrect for the reasons mentioned above.

## Clinical Pearl / High-Yield Fact
A crucial point to remember is that **progestin-only pills** are the preferred choice for breastfeeding mothers. They have a minimal effect on milk supply and are considered safe for use during lactation. Typically, breastfeeding mothers are advised to wait until their milk supply is well established (around 6 weeks postpartum) before starting progestin-only contraceptives.

**Correct Answer: C. Levonorgestrel-only pill.**