Which statement best completes the diagram to explain how geography influenced Greek civilization?

Two boxes are connected by Unidirectional Arrows. Text that reads: Box 1. Cause. Greece was divided by mountains and the Mediterranean Sea. Box 2. Effect.Question Mark.
A.
Individual city-states formed instead of a single kingdom.
B.
The city-states that formed were unable to support themselves.
C.
The Greeks became united under a single government.
D.
The Greeks had no way to protect themselves against invaders.