New weapons such as poison gas, were introduced during world war i that changed how war was fought.
a.
cannons, and pistols
c.
trenches, and rifles
b.
machine guns, and submarines
d.
railroads, and rationing

a is correct

hope this let me know if it is right

        i'm fairly sure that the correct answers are 2 and 3.

        i used both my knowledge of world history and the process of elimination to obtain these answers. option 1 cannot be a possible selection because the mandate of heaven belongs to ancient chinese philosophical belief. option 4 sounds like it would benefit the region than detriment it. however, both 2 and 3 explain a potential reason for what could have contributed to the fall of the roman empire.

      hope this ! if i were you, i'd get a second opinion, because i haven't taken this course for a year. best of luck!

***websites that me understand the curriculum better last year are and ***