**Core Concept:** Varicocele is a dilatation of the pampiniform plexus in the scrotum, usually affecting the left testis due to the anatomical and venous drainage characteristics of the testes.

**Why the Correct Answer is Right:**
Varicocele is primarily caused by abnormal venous drainage from the testes, which results in increased pressure and dilation of the pampiniform plexus. In the male reproductive system, the left testis is more commonly affected due to the following reasons:

1. **Anatomical Differences:** The left testis is generally lower in position compared to the right testis. This position makes it more vulnerable to compression from external factors such as clothing, body posture, or external pressure, leading to increased risk of varicocele formation.
2. **Venous Drainage:** The left renal vein, which is the major contributor to venous drainage from the left testis, has a higher incidence of reflux and backflow due to the close proximity of the left renal vein to the inferior vena cava. This increased venous reflux further contributes to the development of left-sided varicocele.

**Why Each Wrong Option is Incorrect:**
A. While it is true that the right testis has a higher incidence of varicocele, the correct answer is focused on the left side, making it irrelevant for this question.
B. This option mentions the spermatic cord, but the focus is on the venous drainage issues, not the spermatic cord itself.
C. Although varicocele can occur on the right side, the question specifically asks for the reason behind left-sided varicocele, making this option incorrect.
D. This option discusses the testicular artery, which is not directly related to the formation of varicocele due to the venous drainage issues mentioned above.

**Clinical Pearl:**
A varicocele can significantly impact male fertility, as the increased venous reflux and compression may lead to testicular hypoxia and impaired sperm production. Early diagnosis and treatment can help improve fertility outcomes in affected individuals.

In conclusion, the correct answer (A) highlights the anatomical position of the left testis, making it more susceptible to compression and contributing to the development of left-sided varicocele. The other options discuss unrelated aspects of the testes or spermatic cord, which do not directly explain the formation of varicocele on the left side.