This process helps the necessary areas in the body to get the nutrients the blood carries. this is the curculatory system included with the other systems that creates a type of substance or nutrient the body needs.
B. Is what the scientists manipulate in the experiment.
Explanation:
The Independent variable is not dependent, or doesn't rely, on another variable in the experiment. So, it would make the most sense that they would manipulate the Independent so that they can watch and see how the dependent variable reacts to the manipulation, or the change, in the independent variable.
