Explanation:

- Sunil Arora: Correct Answer. In September 2019, Sunil Arora, who was the Chief Election Commissioner of India at that time, assumed the chairmanship of the Association of World Election Bodies (A-WEB) for the 2019-21 term.

- Om Prakash Rawat: He was a former Chief Election Commissioner of India, but there is no relevant connection to A-WEB in 2019.

- Sushil Chandra: He succeeded Sunil Arora as Chief Election Commissioner, but he did not take over A-WEB's chairmanship during this period.

- Ashok Lavasa: He served as an Election Commissioner but was not involved with A-WEB's chairmanship in 2019-21.