Explanation:

- The LPG strategy of 1991 stands for Liberalisation, Privatisation, and Globalisation.

- Option 1: Landmark - Refers to an important stage or event; not applicable here.

- Option 2: Liquid - A state of matter; unrelated to the economic context of LPG.

- Option 3: Legislative – Related to laws or lawmaking; irrelevant to the LPG strategy.

- Option 4: Liberalisation - Removal of restrictions in economic policies to attract private investments. This was significant in the Indian economic reforms of 1991.