A sea abounding in islands

Answer: Option B

One word substitute is Archipelago.

Strait: a narrow passage of water connecting two seas or two other large areas of water.
Archipelago: a sea or stretch of water having many islands.
Ocean: a very large expanse of sea, in particular each of the main areas into which the sea is divided geographically.
Gulf: a deep inlet of the sea almost surrounded by land, with a narrow mouth.