Answer: Option (4)
Explanation: In the given picture, we could see that structure A is an underwater sea mount, where continuous erosion has taken place by the ocean water at a time when the sea level was at a lower height.
This continuous erosion of the top of the sea mount depicts that a part of the previously existing crust has been eroded and after a certain period of time, again the sea level had rise upto some extent. This has no relation to the subduction zone.
Hence, the correct answer here is option (4)