Answer : 3. "Digboi, Assam"
Explanation :

Answer: C) Digboi, Assam Explanation: Digboi has the distinction of being India's oldest continuously producing oilfield. Digboi refinery, now a division of Indian Oil Corporation, had a capacity of about 0.65 MMTPA as of 2003. Digboi is now Headquarter of Assam Oil Division of Indian Oil Corporation Limited, though the crude production is not high today.