Fitnesshealth-related physical fitness is defined as fitness related to some aspect of health. this type of physical fitness is primarily influenced by an individual's exercise habits; thus, it is a dynamic state and may change. physical characteristics that constitute health-related physical fitness include strength and endurance of skeletal muscles, joint flexibility, body composition, and cardiorespiratory endurance. all these attributes change in response to appropriate physical conditioning programs, and all are related to health.

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

how is the word primarily used in this excerpt?

a. to describe the physical characteristics that affect health-related physical fitness
b. to indicate which types of physical fitness but do not change any aspects of health
c. to show that physical fitness is influenced by many things but mostly by exercise habits
d. to explain which types of characteristics are included in health-related physical fitness