Lal Bahadur Shastri served as the Prime Minister of India from ______ to ______.

1964; 1966

The correct answer is Option 3 - 1964; 1966

Lal Bahadur Shastri served as the Prime Minister of India from June 9, 1964, to January 11, 1966.
Lal Bahadur Shastri assumed office as Prime Minister following the sudden demise of Jawaharlal Nehru, the first Prime Minister of India. His leadership came at a critical juncture when India was facing various internal and external challenges.