**Core Concept**
Breast milk storage involves maintaining the optimal temperature to preserve its nutritional and immunological properties. Proper storage prevents bacterial growth and maintains the integrity of the milk's antibodies and nutrients.

**Why the Correct Answer is Right**
Breast milk can be safely stored in a refrigerator at a temperature of 4°C (39°F) for up to 24 hours. This is because the cold temperature inhibits bacterial growth, and the milk remains aseptic. The storage duration can be extended beyond 24 hours if the breast milk is frozen at -18°C (0°F) or below. When refrigerated, breast milk should be stored in a clean, airtight container at the back of the refrigerator to maintain a stable temperature.

**Why Each Wrong Option is Incorrect**
**Option A:** 4 hours is an incorrect storage duration for breast milk in a refrigerator. This duration is more suitable for storing breast milk at room temperature.
**Option B:** 8 hours is also an insufficient storage duration for breast milk in a refrigerator. While it may be safer than storing at room temperature, it does not meet the recommended storage period.
**Option C:** 12 hours is still too short for safe breast milk storage in a refrigerator. This duration does not allow for optimal preservation of the milk's nutritional and immunological properties.

**Clinical Pearl / High-Yield Fact**
When storing breast milk, it is essential to label the container with the date and time of expression, as well as the baby's name. This helps in maintaining the first-in-first-out principle and prevents confusion when feeding.

**✓ Correct Answer: D. 24 hrs**