_____is an industry association and self-regulatory organisation (SRO) whose primary objective is to work towards the robust development of the microfinance sector.

The correct answer is Microfinance Institutions Network.

To understand why this is the correct answer, let's break down the key terms and organizations involved:
1. Microfinance Institutions Network (MFIN): MFIN is an association for the microfinance sector in India. It was established in 2009 and is recognized by the Reserve Bank of India (RBI) as a Self-Regulatory Organisation (SRO) for Non-Banking Financial Company-Microfinance Institutions (NBFC-MFIs). Its primary objective is to promote responsible lending, client protection, and the robust, sustainable development of the microfinance sector by ensuring compliance with regulatory guidelines and ethical code of conduct.
2. NABARD (National Bank for Agriculture and Rural Development): NABARD is an apex development bank in India, established by an Act of Parliament. It is not an industry association or an SRO, but rather a government-authorized regulatory and developmental institution focusing on agriculture and rural development.
3. Self-help Group Association: This is a generic term referring to local community-based groups rather than a formalized national-level industry association or RBI-recognized SRO representing microfinance institutions.
4. Microfinance and Investments Regulatory Authority: This is not a recognized SRO or primary industry association regulating Indian microfinance institutions in this capacity.

Therefore, the organization that fits the description of an industry association and self-regulatory organization (SRO) dedicated to the development of the microfinance sector is the Microfinance Institutions Network.