A physical education instructor was interested in studying possible influences on running. She had heard that teens were more likely to run greater distances if they ran later in the day. To test this out, she challenged each of her three classes (one held at 9:00 am every day [Morning], one at 1:00 pm [Midday], and one at 4:00 pm [Afternoon]) to a running contest where they were instructed to run as far as they could on the track during their one-hour gym class every day for a week. The teacher recorded how far each student had run in miles by the end of the week.

a)What is the IV or GV in the above study, which is it , and how can you tell? Why is it important to determine whether it is an IV or GV?