Final answer:
a. Tobacco was the crop that drove the demographic change in the Chesapeake between 1670 and 1700, as it was highly labor-intensive and required extensive use of enslaved labor, thus altering the region's population.
Step-by-step explanation:
The export crop that drove the drastic demographic change in the Chesapeake between 1670 and 1700 was a. tobacco.
Tobacco was the most lucrative product of the Chesapeake colonies and the primary export of both Virginia and North Carolina.
The cultivation of tobacco was labor-intensive, needing a steady workforce for the hard work of clearing the land, caring for the plants, curing the leaf, and packing the product for export.
This led to the importation of more enslaved laborers, altering the demographic makeup of the region significantly. As a controversial crop, tobacco was so impactful that it faced attempted bans by monarchs in Europe and China.