Answer:
Mice given daily injection of saline solution
Explanation:
Control group are used to make comparism in an experiment because they are standards.
Most experiment have a control group as it is used as a check for the performance of the experimental group. Control group and the experimental groups are usually identical but are not always subjected to any treatment as the case with experimental groups this treatment should have an effect on the outcome of interest while the control group is not.
The mice given vitamin D is the experimental group while the one given saline solution is the control. Saline solution is not the same as vitamin D, saline is a solution of salt and water to sustain the mice it is not a vitamin D treatment hence no change is expected of it but the group with Vitamin D treatment are the experimental group.
