**Core Concept**
The suprarenal veins are responsible for draining the adrenal glands, and their anatomy is crucial for understanding the venous drainage of the retroperitoneal organs. The suprarenal glands receive a dual blood supply from the adrenal arteries, and their venous drainage is primarily into the renal veins.

**Why the Correct Answer is Right**
The left suprarenal vein is unique in that it drains directly into the left renal vein, whereas the right suprarenal vein drains into the inferior vena cava. This is due to the anatomical relationship between the left suprarenal gland and the left renal vein. The left renal vein is longer and more vertical than the right renal vein, allowing it to receive the drainage from the left suprarenal gland. This is a crucial anatomical detail to remember, especially when considering surgical approaches to the adrenal glands.

**Why Each Wrong Option is Incorrect**
**Option A:** The inferior vena cava is the primary drainage site for the right suprarenal vein, not the left suprarenal vein.
**Option C:** The right renal vein is not the drainage site for the left suprarenal vein, as the right renal vein drains into the inferior vena cava.
**Option D:** The portal vein is responsible for draining the gastrointestinal tract and is not involved in the venous drainage of the suprarenal glands.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the left suprarenal vein is longer and more vertical than the right suprarenal vein, which affects its drainage pattern. This anatomical detail can be critical in surgical planning and in understanding the venous drainage of the retroperitoneal organs.

✓ Correct Answer: B. Lt. renal vein