Which of these technologies was able to spread because of the growth of american railroad networks

the electric light bulb
the telegraph
the mechanical harvester
the internal combustion engine

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:

a they donate money to humanitarian causes

c   they volunteer to alleviate suffering

d   they blame all muslims for not being able to keep their fellow muslims in line.