**Core Concept**
The Fick principle of cardiac output calculation is based on the principle of conservation of mass, which states that the rate of oxygen consumption by the body is equal to the rate at which oxygen is delivered to the body. Cardiac output can be calculated using the Fick principle, which takes into account the oxygen consumption rate, the oxygen content of arterial blood, and the oxygen content of venous blood.

**Why the Correct Answer is Right**
The Fick principle of cardiac output calculation does not require the measurement of stroke volume. Instead, it uses the oxygen consumption rate of the body and the difference in oxygen content between arterial and venous blood to calculate cardiac output. This principle is based on the fact that the rate of oxygen consumption is directly proportional to the cardiac output, and the difference in oxygen content between arterial and venous blood is directly proportional to the oxygen extraction ratio. The oxygen consumption rate is a measure of the total amount of oxygen being used by the body, which is affected by factors such as metabolic rate, body size, and activity level. The oxygen content of arterial and venous blood is determined by the partial pressure of oxygen, the hemoglobin concentration, and the oxygen saturation of hemoglobin.

**Why Each Wrong Option is Incorrect**
**Option A:** Whole body oxygen consumption is actually a key component of the Fick principle, as it is used to calculate the cardiac output. Without knowledge of oxygen consumption, it would be impossible to accurately calculate cardiac output using the Fick principle.
**Option B:** Oxygen content of arterial blood is also a critical component of the Fick principle, as it is used to calculate the cardiac output. The oxygen content of arterial blood is determined by the partial pressure of oxygen, the hemoglobin concentration, and the oxygen saturation of hemoglobin.
**Option D:** Oxygen content of venous blood is also a key component of the Fick principle, as it is used to calculate the cardiac output. The oxygen content of venous blood is determined by the partial pressure of oxygen, the hemoglobin concentration, and the oxygen saturation of hemoglobin.

**Clinical Pearl / High-Yield Fact**
The Fick principle of cardiac output calculation is a widely used and clinically relevant method for estimating cardiac output, which is essential for assessing cardiac function and diagnosing cardiovascular diseases. It is a non-invasive method that does not require the measurement of stroke volume or cardiac output directly.

**✓ Correct Answer: C. Stroke volume**