**Core Concept**
The left ureter's anatomical relationships are crucial for understanding its potential risks during surgical procedures. The left ureter is known to be closely associated with several structures that are important to identify during laparoscopic or open surgeries.

**Why the Correct Answer is Right**
The left ureter is closely related to the left gonadal vessels, which include the left ovarian or testicular artery and vein. These vessels are situated in the retroperitoneal space, adjacent to the left ureter, and are often encountered during pelvic surgeries. The superior mesenteric vein is also a relevant structure, as it crosses over the left ureter at the level of the aortic bifurcation. Lastly, the sigmoid mesocolon is a peritoneal fold that attaches the sigmoid colon to the posterior abdominal wall and is in close proximity to the left ureter. The internal iliac artery, specifically the left internal iliac artery, is another important structure that is related to the left ureter, particularly in the pelvic region.

**Why Each Wrong Option is Incorrect**
**Option A:** Quadratus lumborum is a muscle that is located in the posterior abdominal wall but is not directly related to the left ureter. Its proximity to the ureter is not significant enough to be considered a relevant anatomical relationship.
**Option C:** Superior mesenteric artery is not a relevant structure related to the left ureter. Instead, the superior mesenteric vein is the correct association.

**Clinical Pearl / High-Yield Fact**
When performing pelvic surgeries, it is essential to identify and carefully dissect the left gonadal vessels, sigmoid mesocolon, and left internal iliac artery to avoid damaging the adjacent left ureter.

**✓ Correct Answer: B. bde. Left gonadal vessels, Superior mesenteric vein, Sigmoid mesocolon, and Internal iliac artery.**