Answer: the rebuilding of the Great Wall
At that time, the Chinese citizens had to face constant threats from the barbarian that resided on the northern part of their territory.The previously built wall was not strong enough and able to be destroyed by the invaders. Ming Dynasty took the credit of rebuilding and strengthening the structure of the great wall.
Key basic industries, such as railroads, textiles, and steel had barely made a profit. Railroads lost business to new forms of transportation (trucks, buses, and private automobiles, for instance). Coal mining was especially hard-hit, in part due to stiff competition from new forms of energy, including hydroelectric power, fuel oil, and natural gas.
I'm gonna go with B; A, C, B.
Alexander the Great ruled from 331 - 323 BC, the Han Dynasty started in 206 BC and ended in 220 AD, and finally the Mongol empire began in 1206 AD and ended in 1368 AD.
Hope this helps!
More factories opened and now people migrated to urban areas
Answer:Because it made work so much easier for the common reaper
Explanation: makes less work on the fields so it wouldn't take all day
