The mound builders were american indian groups who a. built irrigation systems for farming. b. developed sophisticated art. c. stayed in their own communities. d. flourished in the eastern river valleys.

A i took the edgunuity unit test

Explanation:

answer: the time zones used to be whatever the local authority wanted them to be. one town might have 6am whenever the sun came up and another town had 6am 10 minutes later.  

the trains had a hard time when their orders said to be at a certain point at 6am.  

6am, but who's 6am.  

the railroads got together and set the time zones more or less along the longitude lines across the country.

explanation:

the western roman empire flourished, but the eastern portion of the empire struggled.