The events are presented in chronological order:
1. (B) Drain of Wealth (British colonial period)
2. (D) Monopolies Inquiry Commission (1977)
3. (C) White Revolution (1970s-80s)
4. (A) New Economic Policy - Liberalisation (1991)
Therefore, option (b) is correct.

In an economy, exclusion of _______ may lead to under estimation of the value of Gross Domestic Product (GDP).