Explanation:

- In 1968, the Indian government, led by Prime Minister Indira Gandhi, issued special stamps titled ‘Wheat Revolution’. This initiative was part of the broader Green Revolution that aimed to improve agricultural productivity and food security in India.

- Option 1, 1987, is not related to the initiation of the Green Revolution or the issuance of these stamps. By this time, the Green Revolution had already made a significant impact in India.

- Option 2, 1975, does not align with the major milestones in the Green Revolution, which was already underway and had achieved significant results by then.

- Option 3, 1943, predates the Green Revolution, which started in the 1960s. During this year, India was under British rule and was facing severe food shortages, including the Bengal Famine.