Original:
The Middle colonies is the greatest place for wheat production. They have a great soil and hard-working people to harvest the wheat grain and oats. Middle colonies is the only source of wheat, so they also have a great chance to trade with others.
Reworded:
Wheat production is at its peak in the Middle Colonies. They have great soil and hard-working people to harvest the wheat grain and oats. Since the Middle Colonies are the sole provider of wheat, they have a great chance to exchange their goods with others.