A 50-year-old will most likely be slower than a 20-year-old in ...

[dakota nelson]

A 50-year-old will most likely be slower than a 20-year-old in
 
  running up several flights of stairs.
  mowing the lawn.
  cleaning the house.
  routine activities at work.

Question 2

The term organ reserve refers to
 
  a decline in functioning of major organs, such as the heart.
  the practice of conserving and transplanting solid organs.
  the mechanism that automatically maintains physiological balance.
  the extra capacity available to an organ when subjected to stress.

[stanleka1]

Answer to Question 1

running up several flights of stairs.

Answer to Question 2

the extra capacity available to an organ when subjected to stress.