The geopolitical theory that stressed the strategic advantages of land over sea power is known as the:
a) domino theory.
b) rimland theory.
c) lebensraum theory.
d) heartland theory.

The correct answer is the heartland theory -answer D), which said that the land away from the seas was safer because it could be better defended.

A somewhat opposite theory was the rimland theory - this one was stressing the advantage of lying on the sea.

The other two options refer rather to speficic concepts from modern politics. 

Answer(a) cheap enough for small shops to purchase;