Explanation:

- Lord William Bentinck, as Governor-General, made significant reforms in India to combat social evils.

- Sati-system: Bentinck legally abolished the practice of Sati in 1829, making it illegal for widows to be burned on their husband's funeral pyre.

- Infanticide and human sacrifice: Bentinck took measures to suppress these practices, which were prevalent in some regions.

- Thaggy: He worked to eradicate Thuggee, the practice of organized crime involving robbery and murder.

- Widow remarriage: Bentinck did not address widow remarriage; it was later legalized by the Widow Remarriage Act of 1856, passed during the Governor-Generalship of Lord Dalhousie.

Based on this explanation, the correct answer is:

Option: 4 - Widow remarriage