The answer is a for u but i am not sure there has to be more explanation for this
I believe the correct answer would be that the Incan army traveled through canals.
Hope it helps!
Sorry I know this was 3 days ago but the flooding had left very rich soil that was really good for farming.
Explanation:
Czar ascends to the throne, then WW1 begins, then food and fuel shortages, then the Czar is killed, and last, the Soviet Republic is established.