Based on the information provided in the passage regarding the trade restrictions established by English law in the late 1600s, the option that would have been ILLEGAL is:
B: A merchant in the Maryland Colony unloads fur from a Spanish ship in exchange for corn.
This action would be illegal because the passage indicates that only British ships could be used to import goods into the colonies, and the fur from the Spanish ship would violate that rule. All imports from non-British ships were prohibited under the Navigation Acts as described.