B. The British army could not protect settlers from Native Americans.
Explanation:
King George III forbid colonists from settling in the Ohio River Valley after it was gained by Britain from France because the British army could not protect settlers from Native Americans.
A lot of Native Americans were near the Appalachian Mountains, where the colonists wanted to settle. After the French and Indian War, many of the colonists felt entitled to land and wanted to branch out from their settlements. Great Britain argued that the British army could not protect the settlers if they went that way and even ended up banning being able to settle there.
This obviously made the colonists kind of angry, as they were already sick of being ordered around by Great Britain by this point. Shortly after, Great Britain started putting taxes on products which they tried to justify by saying that British troops were protecting the colonists.
