**Core Concept:** The National Programme for Control of Blindness (NPCB) is a public health initiative in India aimed at preventing and controlling avoidable blindness. It is coordinated by the Ministry of Health and Family Welfare, and NGOs play a crucial role in implementing the programme.

**Why the Correct Answer is Right:**
The correct answer refers to the stage at which NGOs (Non-Governmental Organizations) are involved in the implementation of the National Programme for Control of Blindness (NPCB). NGOs are essential partners in the programme, providing support in various aspects like resource mobilization, capacity building, programme implementation, and research. In this context, the correct answer is "C" which stands for "coordination." NGOs coordinate with the government, other NGOs, and the community to ensure effective implementation of the NPCB.

**Why Each Wrong Option is Incorrect:**
A. "Advocacy" (Option A) refers to the process of promoting a particular cause, which is not directly related to the stage at which NGOs are involved in the NPCB implementation.
B. "Education" (Option B) pertains to imparting knowledge and skills, which is not the specific stage at which NGOs contribute to the NPCB.
D. "Surveillance" (Option D) refers to the systematic monitoring of a population for a particular disease or condition, which is not the main role of NGOs in the NPCB.

**Clinical Pearl / High-Yield Fact:**
Understanding the role of NGOs in the National Programme for Control of Blindness (NPCB) is crucial for medical professionals, as NGOs contribute significantly to the programme's success. Involving NGOs at the stage of coordination ensures effective implementation of the NPCB, leading to better control of blindness and visual impairment in India.