**Core Concept**
Streptococcus pneumoniae is a fastidious, Gram-positive bacterium that requires a specific culture medium to grow. This microorganism is commonly found in the respiratory tract and can cause pneumonia, meningitis, and other invasive diseases.

**Why the Correct Answer is Right**
The correct medium used for growing Streptococcus pneumoniae is blood agar with 5% sheep or horse blood. The blood provides the necessary nutrients, such as heme, for the bacteria to grow. The bacteria are also enriched by the presence of CO2, which helps to maintain an optimal pH for growth.

**Why Each Wrong Option is Incorrect**
**Option A:** Chocolate agar is used for growing Haemophilus influenzae, not Streptococcus pneumoniae.
**Option B:** MacConkey agar is a selective medium for lactose-fermenting Gram-negative bacteria, not suitable for Streptococcus pneumoniae.
**Option C:** Sabouraud agar is used for growing fungi, not Streptococcus pneumoniae.

**Clinical Pearl / High-Yield Fact**
When culturing Streptococcus pneumoniae, it is essential to use a CO2 incubator to maintain an optimal pH for growth, as the bacteria are sensitive to acidic environments.

**Correct Answer:** C.