Answer:
The main idea of the text is to present how the Pony Express made communication in the US easier at a time when the country was experiencing a high growth rate.
Explanation:
The main idea of a text is the main subject that this text addresses and that will govern all the information presented during the text. In the text above, we can see that the main idea is the fact that Pony Express streamlined communication in the US and how this was very beneficial for the country's growth. That's because in the text, we can see that all the information turns on how the creation of Pony Express allowed the correspondence to be delivered much faster.