Stella thinks that if people are exposed ultraviolet light then they are more likely get skin cancer. stella designs an experiment wherein sample a consisted of people were exposed to ultraviolet light and sample b was not.
what is the independent variable?

The amount of UV light exposure.

Explanation:

The independent variable is the one variable that an individual must change during an experiment in order to investigate or test the dependent variable. Basically their relationship to the experiment or between themselves can be easily remembered through their names: The independent variable is the one that's controlled by the researcher and therefore does not depend on other variables from the experiment (amount of UV light), the dependent variable depends on the independent variable since its often the result from the latter's variations (cases where people developed skin cancer) and finally, the controlled variable is the one that's kept the same throughout the experiment (Time exposed to sunlight within group A or method through which patients were tested for skin cancer).