To Test a Hypothesis About a Given Variable, Experimental and Control

Multiple Choice

To test a hypothesis about a given variable, experimental and control groups are tested in parallel. Which of the following best explains the dual experiments?

A) In the experimental group, a chosen variable is altered in a known way. In the control group, that chosen variable is not altered so a comparison can be made.
B) In the control group, a chosen variable is altered in a known way. In the experimental group that chosen variable is not altered so a comparison can be made.
C) In the experimental group, a chosen variable plus all other variables are altered. In the control group, the chosen variable is altered however all other variables are held constant.
D) In the experimental and control groups two different variables are altered.