Question

max is testing how caffeine affects concentration. which variable is the independent variable?
caffeine, because it is measured by max
concentration, because it is measured by max
caffeine, because it is manipulated by max
concentration, because it is manipulated by max

Explanation:

In an experiment, the independent variable is manipulated. Here, Max manipulates caffeine to test its effect on concentration.

Answer:

C. Caffeine, because it is manipulated by Max