**Core Concept**
The body's ability to regulate urea levels is crucial, as urea is a byproduct of protein metabolism that can accumulate in the blood and cause various complications if not excreted properly.

**Why the Correct Answer is Right**
Urea is primarily excreted by the kidneys through a process involving the urea transporter 1 (UT1) in the collecting ducts. UT1 is a sodium-dependent urea transporter that allows urea to be reabsorbed into the bloodstream, and its activity is regulated by antidiuretic hormone (ADH). When ADH levels are high, UT1 activity increases, leading to increased urea reabsorption and decreased urine urea excretion. Conversely, when ADH levels are low, UT1 activity decreases, allowing more urea to be excreted in the urine.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify the role of urea transporters in urea excretion.
**Option B:** This option is incorrect as it does not mention the sodium-dependent nature of urea reabsorption in the collecting ducts.
**Option C:** This option is incorrect as it does not accurately describe the relationship between ADH levels and urea excretion.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize that the kidneys play a critical role in regulating urea levels, and disturbances in this process can lead to complications such as uremia and hyperuricemia.

**Correct Answer: C. Urea is primarily excreted by the kidneys through a process involving the urea transporter 1 (UT1) in the collecting ducts.**