Mainland Greece is a peninsula, which is Text to speech:
A. a mountain range with a river running through it.
B. land that is surrounded by water on three sides.
C. a plain that has no bodies of water within a mile.
D. a marsh that is completely surrounded by rivers.

Option (B)

Explanation:

A peninsula can be simply defined as a distinct geological landform that is covered by water on three of the sides and one side of it interlinked with the mainland area, from which the peninsular area is extended. There are many contrasting peninsula region on earth.

Some of the examples of peninsulas are such as Indian Peninsula, Alaskan Peninsula, Mainland Greece and Scandinavian Peninsula.

Thus, the correct answer is option (B).

because the center-south is called the heart of the country

81 is a composite number.