According to the exercise principle of balance, a workout should
a. address all components of fitness
b. focus on balance and coordination
c. target specific areas for improvement
d. vary exercise activities over time

a. address all components of fitness 

According to the exercise principle of balance, a workout should address all components of fitness.
NOT:
b. focus on balance and coordination 
c. target specific areas for improvement 
d. vary exercise activities over time

According to the exercise principle of balance, a workout should:

a. address all components of fitness 

Explanation:

The Balance Principle dictates that each one training should be properly proportioned so as to realize best results. This broad principle operates at several levels of human performance.
All things moderately apply to sports coaching moreover general health and well being
This principle suggests that the proper mixture of coaching activities, diet, and healthy way habits are needed for the best functioning