Refer to the Description Below

Multiple Choice

refer to the description below:
Erica is running a study to investigate the effect of exercise on insomnia symptoms. She recruits participants who report having experienced insomnia at least once a week and assigns them to either exercise for 30 minutes every day or to read a book for 30 minutes every day.
-How many level/s of the experimental variable is/are there in her study?

A) 30
B) 1
C) 2
D) 60