**Core Concept**
The effective sperm count, also known as the total sperm count, is a critical parameter in assessing male fertility. It is calculated by multiplying the concentration of sperm by the total volume of the ejaculate. This value provides an estimate of the total number of sperm available for fertilization.

**Why the Correct Answer is Right**
The World Health Organization (WHO) defines the normal effective sperm count as 15 million sperm per milliliter (mL) or more, with a minimum total volume of 1.5 mL. This value is based on the fact that sperm concentration and volume are both essential components of the total sperm count. A higher total sperm count increases the chances of successful fertilization during intercourse.

**Why Each Wrong Option is Incorrect**
**Option A:** This value is lower than the normal threshold for effective sperm count.
**Option B:** This value is higher than the normal threshold, but it may still be associated with low fertility due to other sperm quality issues.
**Option C:** This value is not a typical measurement for effective sperm count, which is usually expressed in millions per milliliter.

**Clinical Pearl / High-Yield Fact**
When evaluating male fertility, it is essential to consider not only the total sperm count but also sperm motility, morphology, and the presence of any sperm antibodies. These factors can significantly impact the chances of successful fertilization.

**Correct Answer: C. 20 million sperm per mL.**