In a scientific experiment, the control group is the one that
a. is statistically significant
b. is not manipulated and used for comparison
c. is usually discarded
d. is exposed to a specific treatment to test the effects
e. exerts control over the test subjects

B. is not manipulated and used for comparison

Explanation:A control group is merely a group placed on an experiment for comparing with the experimental group. The control group will receive no treatment and serves as a reference to measure the reactions of the subjects present in the group being tested.

The use of a  control group is necessary for an experiment since the experiment has variables being tested and some other factor may arise in the carrying out of the experiment, that previously was not taken into account. It allows then to eliminate also non-essential variables.

Then researchers can make sure the hypothesis, remaining all variables the same for the tested groups will enable to measure the independent variable and see if this variable is to be held accountable for the results as the outcome of the research.