What you are reading and think what is in the text so you can understand it better.
They were both farmers and the north used more factories while the south didn't.
<span>reason that napoleon's troops </span>
The correct answer is option D. "Companies replaced hand-operated brakes with air brakes on trains". The development of air brakes on trains was a significant improvement of railroad safety. Air brakes function much more faster than hand-operated brakes, because hand-operated brakes required that the brakemen turned the brakes in one car and jump to the next to set the brakes on, and so on.
