Mula sa akdang polina iopd
Answer:
Writing began to disappear and the standardized weights and measures used for trade and taxation fell out of use. Scholars have put forth differing theories to explain the disappearance of the Harappans, including an Aryan Invasion and climate change marked by overwhelming monsoons.
Explanation:
Slaves in colonies worked in rice,tabacco and sugar cane crops the working day were from day to late evening and at night they sleep on benches and on the floor (HOPE THIS HELP YOU)
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.