**Core Concept**
ASHA stands for Auxiliary Nurse Midwife and Auxiliary Nurse and Midwife (ANM) Sub-centre Health Assistant (ASHA) is a part of the National Rural Health Mission (NRHM) in India. The ASHA is a community health worker who acts as an interface between the community and the public health system, playing a crucial role in improving maternal and child health.

**Why the Correct Answer is Right**
The ASHA is posted at the sub-centre level, which is the most peripheral and first contact point between the primary health care system and the community. The ASHA is responsible for motivating and educating women in the community about health and nutrition, and also acts as a liaison between the community and the public health system.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ASHA is not posted at the Primary Health Centre (PHC) level, which is a higher level of health care than the sub-centre.
**Option B:** This option is incorrect because ASHA is not posted at the Community Health Centre (CHC) level, which is a higher level of health care than the sub-centre.
**Option C:** This option is incorrect because ASHA is not posted at the District Hospital level, which is a higher level of health care than the sub-centre.

**Clinical Pearl / High-Yield Fact**
ASHA workers are crucial in improving maternal and child health by providing education and support to women in the community, and also by acting as a liaison between the community and the public health system.

**Correct Answer: C. Sub-centre.**