**Core Concept**
Decreased oxygen delivery to tissue is a critical condition that can lead to cellular hypoxia and tissue damage. It is a complex process involving multiple factors, including cardiac output, hemoglobin concentration, myoglobin levels, and the oxygen-carrying capacity of blood.

**Why the Correct Answer is Right**
The correct answer is related to the factors that affect oxygen delivery to tissue. Oxygen delivery (DO2) is calculated as the product of cardiac output (CO) and arterial oxygen content (CaO2). Cardiac output is the volume of blood pumped by the heart per minute, and arterial oxygen content is the amount of oxygen bound to hemoglobin and myoglobin in the blood. A decrease in cardiac output, such as in heart failure, or a decrease in hemoglobin concentration, such as in anemia, can lead to decreased oxygen delivery to tissue.

**Why Each Wrong Option is Incorrect**
**Option A:** While a decrease in hematocrit can affect oxygen delivery, it is not the most direct factor.
**Option B:** Myoglobin is an oxygen-storing protein in muscle tissue and does not directly affect oxygen delivery to tissue.
**Option C:** Although a decrease in pH can affect hemoglobin's oxygen-binding capacity, it is not a primary factor in decreased oxygen delivery to tissue.

**Clinical Pearl / High-Yield Fact**
A critical factor in maintaining oxygen delivery to tissue is ensuring adequate cardiac output and hemoglobin levels. In patients with compromised cardiac function or anemia, supplemental oxygen may not be sufficient to meet tissue oxygen demands.

**Correct Answer: C. Decreased cardiac output**