Which line from the text best illustrates the "physical endurance" required for the Pony Express?

A time when overland travel was slow and cumbersome

It brought the Atlantic coast and the Pacific slope ten days nearer to each other.

It was a system by means of which messages were carried swiftly on horseback.

It was of the greatest importance in binding the East and West together.

Question

Which line from the text best illustrates the "physical endurance" required for the Pony Express? 

 A time when overland travel was slow and cumbersome 

 It brought the Atlantic coast and the Pacific slope ten days nearer to each other. 

 It was a system by means of which messages were carried swiftly on horseback. 

 It was of the greatest importance in binding the East and West together.

anonymous · Answer

C suggests a lot of hard riding