which sentence or sentences have correct parallel structure? those who choose to climb mt. everest face…

Brief Explanations:

Parallel structure requires items in a list to be in the same grammatical form. In the first sentence, "frigid weather", "high winds", and "altitude sickness" are all noun - phrases, maintaining parallelism. In the second sentence, "extreme weather" and "winds" are noun - phrases, but "altitude" is just a noun without an adjective like the others, so it lacks parallelism.

Answer:

Those who choose to climb Mt. Everest face frigid weather, high winds, and altitude sickness.