Answer:
Reps, A
Step-by-step explanation:
Reps is the right answer.
For example, if I did one push up, thats one rep. If I did 999, thats 999 reps.
Sets and circuits are something different, basically like multiple sets together and multiple reps in all of them is a circuit, which can then be repeated. I do not know what groups are, but it is not relevant.