To test the effect of vitamin d on growth, two groups of rats were raised under identical conditions and fed the same diet. one of the groups received daily injections of vitamin d. the other group received injections of saline, which did not contain vitamin d. all the rats were weighed weekly for 2 months. in this experiment, the control was

The other group received injections of saline, which did not contain vitamin D

Explanation:

A scientific experiment is performed to test the predicted hypothesis of natural phenomenon.

The experiment is designed in which the samples are divided into to groups that are the group which receive the treatment called experimental group and the group which do not receive the treatment and thus remains same throughout the experiment called control experiment.

The control samples are required in the experiment to compare the effect of the dependent variable and thus control group acts as a reference to the experimental group. In the given question, since the test was performed to study the effect of vitamin D on the growth of the rat so the group which will not receive the Vitamin D treatment will be considered a control group.  

Therefore the sample which has received saline instead of vitamin D in the control group.

the answer would be d : p