How does the excerpt further develop the ideas presented in this statement?

yet it [the pony express] was of the greatest importance in binding the east and west together at a time when overland travel was slow and cumbersome, and when a great national crisis made the rapid communication of news between these sections an imperative necessity. (5 points)

a. it illustrates the difficulties associated with travel to the west coast.

b. it suggests that the pony express had some part in the outbreak of civil war.

c. it describes the historical con. text around the country at the time of western expansion.

d. it establishes the relationship between the military and the fierce tribes.