Question

Students investigated four different brands of disinfectant wipes. The students rubbed each brand of wipe on a different desk. They collected a bacteria sample from each wiped desk with a cotton swab, then transferred the bacteria to a petri dish. The students also took a bacteria sample from an unwiped desk. After three days, the students compared the amount of bacterial growth in all five petri dishes. Which of these was the experimental control?

A. the sample with the greatest amount of bacterial growth



B. the sample from the unwiped desk



C. the length of time the bacteria was allowed to grow



D. the number of brands of disinfectant wipes tested

Answer 1

the sample from the unwiped desk