**Core Concept**
The male urethra is a muscular tube that carries urine from the bladder to the outside of the body. It has several anatomical constrictions, which are narrow parts that can affect urinary flow. Understanding the narrowest part of the male urethra is crucial for diagnosing and managing urinary tract disorders.

**Why the Correct Answer is Right**
The narrowest part of the male urethra is the **membranous urethra**, which is a short segment located within the deep perineal pouch. This part of the urethra is narrower due to the surrounding muscles and connective tissue. The membranous urethra is approximately 1-2 cm long and is surrounded by the external urethral sphincter muscle. This narrow segment can be a site of obstruction in conditions such as urethral stricture or prostatic hyperplasia.

**Why Each Wrong Option is Incorrect**
* **Option A:** The prostatic urethra is not the narrowest part of the male urethra, although it is a constricted area due to the surrounding prostate gland tissue.
* **Option B:** The penile urethra is not as narrow as the membranous urethra, although it can be constricted in conditions such as phimosis or urethral stricture.
* **Option C:** The preprostatic urethra is not a recognized anatomical term for a narrow part of the male urethra.

**Clinical Pearl / High-Yield Fact**
The narrowest part of the male urethra is a potential site of obstruction in conditions such as urethral stricture or prostatic hyperplasia. This knowledge is crucial for diagnosing and managing urinary tract disorders.

**Correct Answer:** C. Membranous urethra