Explanation:

- Life Insurance Corporation of India (LIC) is an Indian state-owned insurance group and investment company headquartered in Mumbai.

- The Parliament of India passed the Life Insurance of India Act on 19 June 1956.

- LIC started operating in September of that year.

- The Act consolidated the business of 245 private life insurers and other entities offering life insurance services.

- The nationalisation of the life insurance business in India was a result of the Industrial Policy Resolution of 1956, which created a policy framework for extending state control.

Options Explanation:

- Option 1: who - Typically refers to a person. Not suitable for referring to an act.

- Option 2: when - Relates to time. Doesn't fit contextually in this sentence.

- Option 3: then - Refers to a sequence in time. Does not connect ideas correctly here.

- Option 4: which - Correct for introducing a clause providing additional information about the act.