What is exposed to antigen (virus) hoping to trigger an immune response? (the second letter is c the fourth letter is i and the seventh letter is i. yes this is a crossword)

Ronald wants to see if a new shower cleaner works better in removing soap than his old cleaner. he uses the new cleaner on one half of the shower tiles and his old cleaner on the other half. identify the independent and dependent variables in this experiment. enter your answer in the space provided.