I think you already have this right but other wise id say wind or water
The answer is A. It can be scientifically found while the other answer choices are all peoples personal opinions, not scientific facts like measurement.
Blood Tests
A creatinine level of greater than 1.2 for women and greater than 1.4 for men may be an early sign that the kidneys are not working properly. As kidney disease progresses, the level of creatinine in the blood rises.