**Core Concept**
A Primary Health Centre (PHC) is a crucial component of the healthcare system in many countries, serving as a first point of contact between the community and the healthcare system. For a PHC to become a first referral unit, it must possess specific infrastructure and capabilities to provide comprehensive and specialized care to the community.

**Why the Correct Answer is Right**
A PHC must have a minimum capacity of 20 beds, a laboratory, an operating theatre, a delivery room, and a functional X-ray machine to become a first referral unit. This enables the PHC to provide basic and emergency surgical services, obstetric care, and diagnostic facilities, making it a reliable first point of referral for the community. The presence of these facilities allows the PHC to provide comprehensive care and reduce the need for patients to travel to higher-level facilities.

**Why Each Wrong Option is Incorrect**
**Option A:** A PHC may not necessarily have a full-time specialist or a functional CT scanner to be considered a first referral unit.
**Option B:** A PHC with only 10 beds and basic equipment may not be able to provide comprehensive care, making it unsuitable as a first referral unit.
**Option C:** A PHC may not have the necessary infrastructure or personnel to provide 24/7 emergency services, which is a critical requirement for a first referral unit.

**Clinical Pearl / High-Yield Fact**
It's essential to note that the World Health Organization (WHO) has established guidelines for the minimum requirements for a PHC to become a first referral unit, which includes the presence of a laboratory, an operating theatre, and a functional X-ray machine.

**Correct Answer: C. A PHC with a minimum capacity of 20 beds, a laboratory, an operating theatre, a delivery room, and a functional X-ray machine.