Question

the passage below describes an experiment. on winter mornings, isabelle had to scrape the ice off of the windshield and side mirrors of her car. her friend told her that she should cover her side mirrors with plastic bags overnight to stop ice from forming. one winter night, isabelle secured a plastic bag over one of the side mirrors on her car. she left the other side mirror uncovered. in the morning, she checked the percentage of each mirror that was covered by ice. isabelle repeated this test every night for one week, alternating which mirror she covered each night. complete the sentence. in the experiment, the covered side mirrors were part of a control group an experimental group

Explanation:

In an experiment, the experimental group is the one that receives the treatment (in this case, having plastic bags on the side - mirrors). The control group is the one that does not receive the treatment (uncovered side - mirrors). Since the covered side - mirrors are the ones receiving the 'treatment' of being covered to test the effect on ice formation, they are part of the experimental group.

Answer:

an experimental group