ACE Literature States That You Probably Won't Ever Use the Formula

ACE literature states that you probably won't ever use the formula in real life and you won't be tested on it, so why do you need to understand the Fick Equation? Because the Fick Equation measures:

A) The rate at which the body uses oxygen during physical activity
B) The rate at which the body burns calories during physical activity
C) The relationship between respiratory rate and heart rate during physical activity
D) The rate at which the muscles use glycogen during physical activity