Will only give points if answers are
13. what were the most prized materials in ancient china?

14. what did the ancient chinese keep secret for hundreds of years?

15. why do you think this was advantageous (why did this give china an advantage? )

I can't answer 13, but 14 is silk, ancient China kept secret the way to make silk because (15) it gave them an advantage in trade (the silk road) because other countries would trade their goods for silk since china wouldn't tell them how to make it. Hope this helps!

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: