Gerontologists interested in the effects of age on reaction time have two groups of participants take a test in which they must indicate as quickly as possible whether a probe word is a member of a previous set of words. One group of participants is between the ages of 25 and 45, whereas the other group is between the ages of 55 and 75. The time it takes to make the response is measured. In this study:

A. What is the independent variable?
B. What is the dependent variable?
C. Identify the control and experimental groups.
D. Is the independent variable manipulated, or is it a participant variable?

Do you know the characteristics of an independent variable and those of a dependent variable?

Do you know how a control works and what is its purpose?

If you can answer those, you should answer your question properly.