**Core Concept**
The Revised National Tuberculosis Control Programme (RNTCP) in India emphasizes a systematic approach to tuberculosis (TB) screening, primarily focusing on high-risk populations to detect active cases and prevent further transmission.

**Why the Correct Answer is Right**
The RNTCP's screening strategy targets high-risk groups, including:
* Household contacts of TB patients
* Patients with HIV/AIDS or other immunocompromised conditions
* Individuals with symptoms suggestive of TB (e.g., chronic cough, weight loss, fever)
* People with underlying medical conditions that increase TB susceptibility (e.g., diabetes, chronic lung disease)
Early detection and treatment of active TB cases are crucial to prevent the spread of the disease and reduce morbidity and mortality.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately represent the primary focus of RNTCP's screening strategy.
**Option B:** Screening under RNTCP does not primarily emphasize chest X-rays for all individuals, as this would be impractical and resource-intensive.
**Option C:** While treatment under RNTCP is free, the emphasis is on screening and detection, not treatment alone.

**Clinical Pearl / High-Yield Fact**
In RNTCP, the "DOTS" (Directly Observed Treatment, Short-course) strategy is used to ensure adherence to TB treatment regimens, which includes regular monitoring and follow-up of patients to prevent defaulting from treatment.

**Correct Answer: D. High-risk groups. High-risk groups.**