Explanation:
A. a measure of heat energy in food
By he NIH trying a new drug to help reduce pain associated with sickle-cell anemia, it's an example of an "experiment".
An experiment involves a hypothesis (an educated guess as to what's going to happen) and trying out the hypothesis and finding the solution.
The answer is C)
Backflow prévention device
Lactic acid build-up was the cause of muscle fatigue.
