The economic development of the mid-atlantic, new england, and southern colonies differed mainly because of climate (the north colonies were much more cold than the southern, which limited the amount and the types of plants they can grow), soil (northern soil was not as fertile as southern), resources found (there were greater amounts of fishes in the north then south, and so the Northern colonists built up a "fish economy" instead of farming.)
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The answer is b: the native people lacked natural immunities
