Individuals need to adjust their physical activity to account for as they age.
a. reduced flexibility
b. decreased energy levels
c. a loss of balance
d. all of the above

Individuals need to adjust their physical activity to account for reduced flexibility, a loss of balance, as well as decreased energy levels as they age. As we see, there is a number of rather unwanted changes which happen with old age so the correct answer would be D - all of the above. 

Individuals need to adjust their physical activity to account for reduced flexibility, decreased energy levels, and a loss of balance as they age.