Answer:
B.finding friends who like to exercise the same way you do
Step-by-step explanation:
Not mandatory, or not necessary are two very close things, finding friedns that like to exercise the same way as you do could be important and helpful on your exercising habits, but without this you can still go out and exercise, if you do not check with the doctor first which exercises can harm you, you could injure yourself, as well as when not using appropraite protective equipment or clothing that is designed to match your exercise, so the only one that is not necessary would be B.finding friends who like to exercise the same way you do