**Core Concept**
The question is testing the understanding of the primary unit of health care delivery, which encompasses preventive, curative, and promotive services. This concept is crucial in public health and primary care medicine.

**Why the Correct Answer is Right**
The Community Health Centre (CHC) is the optimum unit of preventive, curative, and promotive health care. This is because CHCs provide comprehensive health services, including preventive programs, curative treatments, and health promotion activities, making them the ideal unit for delivering primary health care. CHCs also serve as referral centers for primary health centers and other peripheral health facilities.

**Why Each Wrong Option is Incorrect**
**Option A:** Primary Health Centre (PHC) - While PHCs are the first contact point for the population with the national health system, they may not have the capacity to provide comprehensive health services, making them less than ideal for delivering all three types of health care.
**Option B:** Sub-Centre - Sub-centers are the most peripheral and basic units of health care delivery, primarily providing preventive and promotive services. They may not have the resources or infrastructure to provide curative services.
**Option C:** District Hospital - District hospitals are secondary-level health facilities that provide specialized curative services but may not have the capacity to deliver comprehensive preventive and promotive health care services.

**Clinical Pearl / High-Yield Fact**
The CHC is a critical component of the National Health Mission (NHM) in India, aimed at strengthening the rural health infrastructure and providing accessible health care services to the rural population.

**Correct Answer:** C. Community Health Centre.