Researchers conducted an experiment to identify the effects of three different hand sanitizers on the growth of bacteria. the researchers grew one type of bacteria in twenty-four identical covered petri dishes. then, they opened eighteen petri dishes and applied the three hand sanitizers to six petri dishes each. they left the remaining six petri dishes closed as a control group. when the researchers measured the growth of bacteria two days later, the six dishes that had no hand sanitizer showed the least amount of bacterial growth. the researchers concluded that not using any hand sanitizer would lead to the least bacterial growth. which statement best explains why the researchers’ conclusion was not justified? the experiment tested too many variables. the control group was not treated the same as the experimental group. the sample size of twenty-four petri dishes is not large enough. the single type of bacteria is not adequate to make any conclusions.

The control group was not treated the same as the experimental group.

Explanation:

As you can see in the description above, the researchers have four group of samples:

Group 1: Six petri dishes with hand sanitizer A.

Group 2: Six petri dishes with hand sanitizer B.

Group 3: Six petri dishes with hand sanitizer C.

Group 4: Six petri dishes with no hand sanitizer.

Group 1-3 are the experimental groups, while Group 4 is the control group. While all these experimental groups are left opened for two days, the control group's dishes are closed.  

This creates a confounding variable – an unaccounted variable that might contribute to the changes to the dependent variable (the petri dishes). It might be that the number of bacteria growth is instead caused not by the hand sanitizers – it is instead caused by the open air exposure. Thus option (B) is correct.  

The correct answer is alternative D.

Explanation: The single type of bacteria is not adequate to make any conclusions, since there are multiple types of bacteria that are resistant to many different aspects. Maybe, the kind of bacteria studied is tolerant to hand sanitizers, since the groups treated with hand sanitizers grew more than the ones that didn't have any hand sanitizers in it. This shows that the bacteria could be feeding on the hand sanitizers or that they developed a mechanism to reproduce faster than they would normally reproduce without any kind of environmental pressure. Making generalizations about this specific case would be incorrect then, having no other conditions taken in consideration.

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