In a controlled experiment, an independent variable (the cause) is systematically manipulated and the dependent variable (the effect) is measured; any extraneous variables are controlled. The researcher can operationalize (i.e. define) the variables being studied so they can be objectivity measured.
C.) T<span>he DNA unravels to make two strands </span>
Actually, it is false. P-waves arrive first and then S-waves arrive.