Vignette #2 Jill Is 32 Years Old, and After Years

Vignette #2 Jill is 32 years old, and after years of a mostly sedentary life is determined to get into shape. She decides to take up jogging but cannot decide whether to jog at a moderate pace or very fast pace, and has no idea how long to continue. Jill also wants to learn to monitor her heart rate and pulse. She was a gymnast in high school but can no longer touch her toes. Let's see if you can suggest how Jill should get started by answering these questions. When Jill engages in activities of low to moderate intensity for greater than 20 minutes at a time, her muscles' main source of energy is:

A) fat.
B) glucose.
C) glycogen.
D) phospholipids.
E) Coenzyme Q₁₀.