**Core Concept**
The question tests the understanding of **organ blood flow** and **regional circulation**. It requires knowledge of how blood is distributed to different organs at rest.

**Why the Correct Answer is Right**
The **kidneys** receive a significant proportion of cardiac output, approximately 20-25%, due to their essential role in **filtration** and **waste removal**. This high blood flow is necessary for the kidneys to maintain **glomerular filtration rate (GFR)**.

**Why Each Wrong Option is Incorrect**
**Option A:** The **brain** has a high metabolic rate, but its blood flow is relatively constant and not the highest in terms of ml/kg/min.
**Option B:** The **liver** has a dual blood supply, but its overall blood flow is not the highest on a per-weight basis.
**Option D:** The **skeletal muscle** has variable blood flow depending on activity level, but at rest, it does not receive the highest blood flow.

**Clinical Pearl / High-Yield Fact**
Remember that the **kidneys** are very sensitive to changes in blood pressure and flow, making them prone to injury in states of **hypotension** or **hypertension**.

**Correct Answer:** D. Kidneys.