The main source of revenue for 'not for profit' organisation is:

Not-for-profit organizations focus on missions, not profit. Main revenue sources include:

Option 1: Sale of goods → Usually not primary for non-profits.
Option 2: Sale of periodicals → Can be relevant but not main source.
Option 3: Subscription from members → Primary source for many non-profits.
Option 4: Sale of assets → Rarely a consistent revenue source.

Correct answer: Option 3.