How cold is it when "to build a fire" opens?

Excerpt from the right decision lindsay rock telling a

Asap which sentence features a correctly identified compound pronoun in a prepositional phrase? a.while waiting in line, sara stood near him and her. b.she and i will be at the park on tuesday, waiting for mariah and them. c.everyone is so sure that he'll be late after traveling with peter and maria. d.after they visit the grand canyon, tianna and mom are going to a spa.

What point is the author trying to make by comparing the travel times of the first transcontinental railroad and the first transcontinental flight?