Read the following context and choose the best option to answer the question.
Context: Also , on Thursday , because I was not feeling well , I did n't run . I caught up on Sunday ( though not with running , but by moving furniture and boxes up and down two flights of stairs continuously for 3 hours . I was too exhausted to move afterwards , let alone run !
Question: What may be the reason for using the stairs ?
Options: 
A. They building has easy to use staircases .
B. None of the above choices .
C. They did nt know how to use the elevator .
D. They used it as exercise to work up a sweat .


B