In an Experiment,researchers Wanted to Know Whether Changing the Level

In an experiment,researchers wanted to know whether changing the level of lighting in a factory would have an effect on the productivity of employees.In order to address this question,employees were randomly assigned to three separate identical work areas,but the lighting was set at a different level in each of the work areas.Then employees in all three work groups began to operate machinery that produced small electrical components.The number of components produced by each group was carefully tallied at the end of each 8-hour shift.In this example,the independent variable is .

A) the level of lighting
B) the employees chosen to participate in the experiment
C) the number of components produced
D) the machinery operated by the employees
E) the presence or absence of the researchers