A County is a territory of a country generally for administrative purposes. County comes from the French "<em>conté</em>" meaning jurisdiction of a count.
In the United States, a County is a political subdivision of a state, and its power of government and responsibilities varies widely from state to state, but usually rest in the "<em>county seat</em>" (a municipality), although sometimes could have several or no seats, and sometimes the county seat is just a big settlement.
So County responsibilities fluctuate, i.e. certain counties are governed by an elected body, which name might vary, as in "<em>the county commission</em>" or "<em>county council</em>", or "<em>county court</em>"; and in some states of Midwest, they exercise local powers, and across the United States certain counties might hold additional self-governing municipalities.
Thus the best answer would be (C): <em>Counties' responsibilities can vary based on their locations</em>.