By citizens can affect the direction of their government.

I think the answer is  A. Voting

Explanation:

Paying taxes doesn't affected the direction of the government, serving in the armed forces doesn't change the direction of the government, and serving in the jury doesn't change the direction of the government. Voting can cause new leaders to be elected which can directly change the direction of the government.

these civilizations were located around fertile rivers, where they could produce an abundance of crops