Isthmus is___________?

A. A lagoon
B. An inland Sea
C. An island in a river
D. Narrow piece of land  connecting larger land areas

An isthmus is a narrow piece of land connecting two larger areas across an expanse of water by which they are otherwise separated. A tombolo is an isthmus that consists of a spit or bar, and a strait is the sea counterpart of an isthmus.