## Core Concept
The question requires the application of the Fick principle to calculate cardiac output. The Fick principle states that the total uptake of oxygen by the body per unit time is equal to the product of the cardiac output and the arteriovenous oxygen difference. This can be expressed as: Oxygen consumption = Cardiac output * (Arterial oxygen content - Venous oxygen content).

## Why the Correct Answer is Right
To calculate cardiac output using the Fick principle, we first need to determine the arteriovenous oxygen difference. The arterial oxygen content is given as 20.0 vol% (which can be assumed to be from the aorta), and the mixed venous oxygen content can be best represented by the pulmonary artery O2 content, which is 15 vol%. The arteriovenous oxygen difference is then 20.0 - 15.0 = 5 vol%. The oxygen consumption is given as 400 ml/min.

The Fick principle formula can be rearranged to solve for cardiac output: Cardiac output = Oxygen consumption / (Arterial oxygen content - Venous oxygen content).

Converting vol% to ml/100ml blood, 1 vol% = 1 ml/100ml blood. So, 5 vol% = 5 ml/100ml blood.

Cardiac output (L/min) = Oxygen consumption (ml/min) / (Arteriovenous oxygen difference (ml/100ml)) * 100.

## Why Each Wrong Option is Incorrect
**Option A:** This option would be incorrect based on incorrect calculation or incorrect values used for arterial and venous oxygen content difference.
**Option B:** Similarly, this would not align with correct application of Fick's principle and given data.
**Option C:**
## Clinical Pearl / High-Yield Fact
A key point to remember is that the mixed venous oxygen content is best represented by the pulmonary artery oxygen content, which reflects the complete mixing of blood from the superior and inferior vena cava.

## Correct Answer Line
**Correct Answer: C. **