Regarding research methods, what is a variable? What's the difference between an independent and dependent variable? What is a control group?
A) A variable is a constant factor in research, and there is no difference between independent and dependent variables.
B) An independent variable is manipulated, a dependent variable is observed, and a control group is not necessary in social research.
C) A variable is an unchanging factor, and both independent and dependent variables are the same.
D) An independent variable is manipulated, a dependent variable is observed, and a control group provides a baseline for comparison.