**Core Concept**
The Revised National Tuberculosis Control Programme (RNTCP) has specific guidelines for diagnosing tuberculosis (TB) based on sputum examination. The case definition is crucial for initiating treatment and preventing the spread of TB.

**Why the Correct Answer is Right**
The correct answer is based on the RNTCP guidelines, which classify TB cases based on the presence of acid-fast bacilli (AFB) in sputum. The presence of AFB in sputum indicates the presence of TB bacteria, making it a definitive criterion for TB diagnosis. The RNTCP guidelines categorize TB cases into new and previously treated cases, as well as relapse and treatment failure cases.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the RNTCP guidelines for sputum examination.

**Option B:** This option is incorrect because it does not define the case criteria for TB diagnosis based on sputum examination.

**Option C:** This option is incorrect because it does not accurately describe the RNTCP guidelines for sputum examination.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the presence of AFB in sputum is a definitive criterion for TB diagnosis, and it is essential to follow the RNTCP guidelines for accurate case classification and treatment initiation.

**Correct Answer: B. Smear positive sputum examination for AFB.**