Smithers thinks that a special juice will increase the productivity of workers. He creates two groups of 50 workers each and assigns each group the same task (in this case, they are stapling papers). Group A is given the special juice to drink while they work. Group B is NOT given the special juice. After an hour, Smithers counts the # of stacks of papers each group has made. Group A made 1,587 stacks; Group B mad 2,113 stacks. WHAT IS THE INDEPENDENT VARIABLE? Please Help!