## Core Concept
The World Health Organization (WHO) periodically updates its reference values for semen characteristics. The 2010 update provides a standardized threshold for what is considered a normal sperm count, aiding in the diagnosis and assessment of male infertility.

## Why the Correct Answer is Right
The WHO 2010 criteria for a normal sperm count is ≥ 15 million sperm per milliliter (mL) of ejaculate. This value is crucial for evaluating male fertility. A count below this threshold may indicate oligospermia, a condition associated with male infertility.

## Why Each Wrong Option is Incorrect
- **Option A:** Less than 15 million/mL would be considered low and not within the normal range as per WHO 2010 criteria.
- **Option B:** This option does not provide a specific value and thus cannot be directly evaluated.
- **Option D:** Greater than 20 million/mL, while potentially indicating a healthy sperm count, does not represent the minimum threshold for what is considered normal.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the WHO criteria are used globally for assessing semen quality. A normal sperm count of ≥ 15 million/mL is essential for fertility but does not guarantee fertility on its own; other factors like motility and morphology also play critical roles.

## Correct Answer: C. ≥ 15 million/mL.