Which best describes the purpose of a controlled experiment?
a. to make sure the results of the experiment support the hypothesis
b. to prevent a dangerous condition resulting from a reaction
c. to examine whether one variable causes a change in another
d. to prevent an undesired change in a variable

C. to examine whether one variable causes a change in another.

Explanation:

A controlled experiment is the one where a control variable is used which is used as a benchmark or standard for comparing the changes occurring in a dependent variable due to the changes occurring in an independent variable by undergoing manipulation and alteration.

On the basis of the above explanation, C. to examine whether one variable causes a change in another is the correct option.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.