How long was the development process of the machine for crushing stone

Well based on the fact that the very first patented rock crushing machine was made in the year 1830, and the first successful, Eli Whitney Blake's, was in 1858, I'd say the development process was around 30 years.

        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 ***

the correct answer would in fact be b. (: