Answer:
The correct answer will be option-B.
Step-by-step explanation:
A scientific experiment must contain three variables: independent variable (which can be manipulated), dependent variable(which can be tested) and control (which is kept constant).
Experimental samples must be divided into two groups: an experimental group in which variable to be studied is tested and a control group in which the independent variable does not influence the experiment.
In the given question, since experimental design contains variables and the experimental as well as the control group which act as a reference group to the experiment.
Therefore, Option-B is the correct answer.