A person presents with pneumonia. His sputum was sent for culture. The bacterium obtained was gram positive cocci in chains and alpha haemolytic colonies on sheep agar. Which of the following will help in confirming the diagnosis?

**Core Concept**
The question requires identification of a gram-positive coccus that exhibits alpha hemolysis on sheep agar, which is a key characteristic of *Streptococcus pneumoniae*. This bacterium is a common cause of pneumonia.

**Why the Correct Answer is Right**
*Streptococcus pneumoniae* is known for its alpha hemolytic colonies on blood agar, which means it partially breaks down the hemoglobin in red blood cells, giving a greenish discoloration around the colonies. The correct answer is related to the identification of this species, likely through a specific test.

**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it doesn't relate to the specific identification of *Streptococcus pneumoniae*.
**Option B:** Similarly, this option does not provide a method for confirming the diagnosis of *Streptococcus pneumoniae*.
**Option C:** This choice is also incorrect as it doesn't correspond to a standard method for identifying this bacterium.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that *Streptococcus pneumoniae* is sensitive to optochin (ethylhydrocupreine) and this can be used as a diagnostic tool.

**Correct Answer:** D. Optochin sensitivity test.

✓ Correct Answer: B. Optochin