Shawn is planning a scientific experiment. he wants to learn whether time of day has an effect on how far the roses in his mother's garden are open. he plans to measure the diameter of each flower on three rosebushes every hour during a week in the spring. what is the test variable (independent variable) in shawn's experiment?
a. the time of day
b. the number of flowers
c. the diameter of the flowers
d. the time of year