I'm guessing C bc it is the only one that has something to do with moods.
Myofibrils are bundles of contractile filaments which are arranged in parallel groups in thecytoplasm of striated muscle cells.
The statement that myofibrils do the actual movement during exercise is true. because the main function of the myofibril is to perform muscle contraction, and muscle contractions are the actual movements of the muscles.
Physical activity has mental, emotional and social health benefits.
Answer:
Option C
Explanation:
BMI stands for "Body Mass Index" or option C. BMI is basically a way to tell a person if he or she is underweight, normal weight, or overweight. In order to calculate BMI you need the persons height and weight and use the formula. Which involves exponents and dividing the persons mass and weight to tell if that person is overweight.

Hope this helps.
Its B. they make you heart beat faster cuz aerobic basically means 'air' so