**Core Concept**
The World Health Organization (WHO) provides guidelines for semen analysis, including minimal sperm count, to assess male fertility. These guidelines are based on **sperm parameters** such as concentration, motility, and morphology. The WHO periodically updates these guidelines to reflect current knowledge and laboratory standards.

**Why the Correct Answer is Right**
The correct answer is based on the WHO's updated guidelines, which aim to standardize semen analysis and provide a reference point for clinicians to evaluate male fertility. As of the 4th edition of the WHO laboratory manual, published in 1999 and updated thereafter, the minimal sperm count for a normal semen sample is considered to be **15 million sperm per milliliter**. This value is chosen because it represents a threshold below which fertility potential is significantly reduced.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not align with the WHO's guidelines for minimal sperm count.
**Option B:** Similarly, this option does not match the established threshold for normal sperm count.
**Option D:** This option also does not correspond with the WHO's recommended value for minimal sperm count.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that a sperm count below the WHO threshold can indicate **male infertility** or **oligozoospermia**, and further evaluation and treatment may be necessary. Clinicians should always refer to the most current WHO guidelines for semen analysis.

**Correct Answer:** B. 15 million/ml