Explanation:

- In the mid-1930s, the demand for a Constituent Assembly gained momentum in India.

- The Indian National Congress made this demand a part of their political strategy.

- This demand was formalized at the 1936 session of the Indian National Congress.

- Option 4: Fezpur - This is the correct answer. The session at Fezpur in 1936 saw the demand for a Constituent Assembly.

- Option 1: Kanpur, Option 2: Lahore, Option 3: Bombay - These locations are historically significant but are not tied to the specific event of demanding a Constituent Assembly in 1936.