Correct option is (a) GFR via Blood Test
The explanation: Glomerular Filtration Rate (GFR) is used to test if the kidneys are functioning normally. In kidneys, the glomerulus is the site for ultrafiltration, i.e. filtration of blood under high pressure. Everything except cellular components moves out in this phase and the required materials are reabsorbed in the following phases. Thus, if the glomerulus is not functioning well, unwanted wastes like creatinine will be high in the blood which will all get reflected in the GFR. Thus, the doctors will be able to suggest if the person needs to go for dialysis or not.