In a recent experiment, anti-bacterial hand sanitizer was compared to hand soap. Students washed their hands using the sanitizer or soap and warm water for two minutes; then they dried their hands with a paper towel. The standard of comparison was rubbing hands vigorously for 2 minutes in warm water, without any soap or sanitizer, and then drying with a paper towel. The sanitizer advertisement claimed to kill bacteria more effectively than any soap. After washing, hands were swabbed and then the swab applied to a culture plate and incubated. Finally, the bacterial cultures were counted. Students using the antibacterial santizer had the lowest bacterial culture count. What is the control in the experiment? A) washing with soap B) rubbing vigorously C) the time: two minutes D) rubbing hands in warm water