Kaylee reads an article that states that the frequency of chirping by crickets is related to the temperature of their environment. She wants to conduct an experiment to see if this is true. Kaylee states this hypothesis: Crickets chirp more frequently when the temperature of their environment increases. What is the test variable (independent variable) and outcome variable (dependent variable) in Kaylee's experiment?

A. test variable (independent variable): temperature of environment; outcome variable (dependent variable): frequency of chirping

B. test variable (independent variable): number of crickets; outcome variable (dependent variable): frequency of chirping

C. test variable (independent variable): number of crickets; outcome variable (dependent variable): temperature of environment

D. test variable (independent variable): frequency of chirping; outcome variable (dependent variable): temperature of environment