Linden conducted a simple experiment. 90 participants will be randomly assigned to participate in one of three different exercise programs (yoga, running, and swimming). After the exercise program, participants will report once on their level of enthusiasm to continue on with the program on a Likert scale from 1 (none) to 7 (a alot). How many levels does Linden's independent variable have? Group of answer choices 1 3 7 90