Answer: I believe it would be letter (b)
Explanation: I had to answer this question yesterday and I am pretty sure this is the answer. Because it asks ¨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?¨ so this is really the only plausible answer regarding the question.
C: Because he made significant discoveries about electricity,
"only landscapes" would turn to "videos that have only landscapes"
Most appropriate salutation is Dear or their title like Sir, mr, mrs, and ms
