Which AAMC practice item is this from? It makes it hard to properly answer your questions if you do not post a reference or more passage information.
As the explanation to the Q71 states, aldosterone is a hormone secreted by the adrenal cortex. So, while the hormone effects are in the kidney, excess aldosterone would indicate a problem with the adrenal glands. Thus, normal kidneys would do nothing to correct the problem.
As for Q73, can you post a quick summary of the hypothesis? As it stands, your choice is choice D, which is not logical. By clamping an artery in the body, how would that reduce the total volume of fluid in the body? where is the fluid going that would explain a sudden drop in volume?