Correct Option (A)
Sumatra
Sumatra is geographically the closest major landmass to Great Nicobar. Great Nicobar, the southernmost island of the Nicobar Islands archipelago, is situated in the Indian Ocean, directly north of Sumatra, which is a large island of Indonesia.
Incorrect Options
Borneo: This island is located significantly further to the east of Great Nicobar within Southeast Asia, making it geographically more distant than Sumatra.
Java: Java is another major Indonesian island, positioned to the southeast of Sumatra. Its location places it at a greater distance from Great Nicobar compared to Sumatra.
Sri Lanka: This island nation is located southwest of the Indian subcontinent and is considerably farther from Great Nicobar than Sumatra. Its geographical position is distinct from the Andaman and Nicobar chain.