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 and recorded in the data table. students concluded that the hand sanitizer was most effective in killing bacteria. how would you respond to the students' conclusion? a) the conclusion is valid; the sanitizer plates had higher numbers. b) the conclusion is not valid; there were fewer bacteria cultures on the soap plates. c) the conclusion is not valid because the warm water was as effective as the sanitizer. d) the conclusion is valid because the sanitizer had a better kill rate than the soaps.