Question: The Indian Air Force's rank structure is based on that of the Royal Air Force, the highest rank attainable in the Indian Air Force is Marshal of the Indian Air Force, conferred by the President of India, MIAF Arjan Singh is the only officer to have achieved this rank, he was an Indian Air Force marshal who served as Chief of the Air Staff from 1964, to which year?
Sentence (from "Arjan Singh"): He was Lieutenant Governor of Delhi from 1989 to 1990.
Relevant evidence: No