In which year were four new Directive Principles added to the original list?

The correct answer is 1976.

The Directive Principles of State Policy (DPSP) are enumerated in Part IV of the Constitution of India, from Articles 36 to 51. The original list of Directive Principles has been amended over time to add new principles.

In 1976, the 42nd Amendment Act added four new Directive Principles to the original list. These new principles require the State to:
1. Secure opportunities for the healthy development of children (Article 39).
2. Promote equal justice and provide free legal aid to the poor (Article 39A).
3. Take steps to secure the participation of workers in the management of industries (Article 43A).
4. Protect and improve the environment and safeguard forests and wildlife (Article 48A).

Therefore, the year in which the four new Directive Principles were added is 1976.