Why Is It Optimal for a Researcher to Ensure That

Multiple Choice

Why is it optimal for a researcher to ensure that only one variable changes throughout an experiment?

A) Because more than one variable creates a statistical nightmare that is exceedingly difficult to interpret.
B) Because multiple variables will require more research participants, and thus more funding.
C) Because more than one variable changing can influence our results and lead to incorrect conclusions.
D) Because the definition of a true experiment is that only one variable should change at a time; otherwise, it is not an experiment.