Aresearcher wants to know whether children eating a high-protein breakfast will have a higher test grade. half of the children in the study eat a high-protein breakfast while the other half eats their normal diet. the control group consists of the children who

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In an experiment to know whether children eating a high-protein breakfast will have a higher test grade, and half of the children in the study eat a high-protein breakfast while the other half eats their normal diet. the control group consists of the children who eat their normal diet. 

Control groups are commonly used in research and are the basis for making comparisons in an experiment. The control group is the one to which no special treatment is applied.

In this case, the control group would be the children who are eating their normal diet. The results will compare the grades from the students with a high-protein breakfast with this group, to see which diet gets better results, or to see if the diet doesn't influence the test grades.