The correct option is B Isthmus
Peninsula : a piece of land almost surrounded by water or projecting out into a body of water.
Isthmus : a narrow strip of land with sea on either side, forming a link between two larger areas of land.
Continent : any of the world's main continuous expanses of land (Europe, Asia, Africa, North America, South America, Australia, Antarctica).
Gulf : a deep inlet of the sea almost surrounded by land, with a narrow mouth.
Hence, option (B) is correct.