When you flex your muscles you are contracting them. When your muscle fibers gain tension through Actin and Myosin crossbridge cycling they may shorten due to the tension. This is called muscle contraction
The best answer would be B because, for instance, if someone is bothering you and you tell the teacher, you say how you feel if you don't know, it just wouldn't make sense. You get what I am trying to say right?
I hope this helps:)
B. Sleep Disorders because thats mental
