**Core Concept**
The question is testing the understanding of a complication associated with Trans Urethral Resection of Prostate (TURP), a procedure used to treat benign prostatic hyperplasia (BPH). This concept involves the anatomical and physiological changes that occur during TURP and the potential consequences of these changes.

**Why the Correct Answer is Right**
The most common cause of delayed urinary tract obstruction after TURP is the formation of TURP syndrome or more specifically TURP syndrome is caused by absorption of irrigation fluid containing glycine or other substances. However, the correct answer is related to the formation of blood clots. Blood clots can form in the prostatic urethra due to the bleeding that occurs during the procedure. These clots can obstruct the urethra and lead to delayed urinary tract obstruction. The formation of blood clots is a well-known complication of TURP and can be a serious condition if not treated promptly.

**Why Each Wrong Option is Incorrect**
* **Option B:** This option is incorrect because while urethral strictures are a potential complication of TURP, they are not the most common cause of delayed urinary tract obstruction.
* **Option C:** This option is incorrect because while urinary retention is a potential complication of TURP, it is not a cause of delayed urinary tract obstruction.

**Clinical Pearl / High-Yield Fact**
It is essential for surgeons to take steps to prevent blood clot formation during TURP, such as using a continuous irrigation system and ensuring that the patient is adequately anticoagulated.

**Correct Answer:** C. Blood clots.