Physical activity is an inclusive term that refers to any expenditure of energy brought about by bodily movement via the skeletal muscles; as such, it includes the complete spectrum of activity from very low resting levels to maximal exertion. exercise is a component of physical activity. the distinguishing characteristic of exercise is that it is a structured activity specifically planned to develop and maintain physical fitness.

"exercise" britannica school. encyclopaedia britannica, inc., 2013. web. 21 oct. 2013.

how is the word spectrum used in this excerpt?

a to identify the characteristics of low resting activity levels
b to show that there are a wide range of possible physical activities
c to describe the amount of activity required for maximal exertion
d to indicate that a physical activity requires a body to use energy