Read this sentence from "The Final Assault."
My thirty-pound load seemed to crush me downward and stifled all enthusiasm, but when I turned on the oxygen and breathed in deeply, the burden seemed to lighten and the old urge to get to grips with the mountain came back.
In this sentence, the narrator gives an example of why oxygen is vital to climbers on Mt. Everest. How does the narrator develop this concept in the rest of the narrative?
A. by explaining how climbers carry their oxygen equipment
B. by showing instances where a lack of oxygen affects climbers
C. by describing times when climbers used oxygen while climbing
D. by giving details about how oxygen equipment can malfunction
