As people enter old age, some of the changes the body undergoes includes:

a. deteriorating eyesight
b. decreased strength
c. less flexibility
d. all of the above

The answer is d. The body has more problems trying to keep the body maintained. The more the person is active helps the body maintain its function.

35 cubic feet of dirt if it's digging a burrow

The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)