Which allowed farmers to plow fields using horses? a heavy plow with a horse collar
a new trade route created more fields
a heavy plow with an oxen collar
a surplus in horses from nearby farms

the answer is a heavy plow with a horse colar

(d) rivers.

explanation:

civilizations developed around rivers because their waters provided places to hunt and fish. also, as the rivers flooded, the lands around them became fertile. this allowed them to support farming. this is especially true of the nile river, which flooded the same time each year.

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