Acoastline is a narrow sea between two close landmasses .

FALSE

Explanation:

A coastline is usually defined as a long extending land that occurs along the edges of the oceans and seas. These are formed due to the deposition of the sediments from the rivers that join the seas and also due to the deposition of the sediments from the seas. The coastlines are generally considered to be the meeting point of land areas and the seas.

But, a strait or a channel is described as a narrow type of channel that runs between any two close landmasses.

Thus, the above statement is False.