Answer : 4. "Bangladesh"
Explanation :

Recently, the 4th edition of bilateral exercise, Bongosagar-23 and the 5th edition of Coordinated Patrol (CORPAT) between the Indian and Bangladesh Navies took place in the North Bay of Bengal. During the exercise, ships and aircraft from both the navies jointly patrolled the International Maritime Boundary Line (IMBL) and engaged in maritime exercises to promote interoperability.