In this case, I would say my answer is that the colonies lost territory. However, it also is true that Britain gained territory. Why? Well, see below!
The French and Indian War was a battle fought between the French and the British over possession of the Ohio River Valley. The war included the word “Indian” in it because in this battle, Indians were known for allying with both France and Britain. However, the French lost. In result of their loss, the British not only gained the Ohio River Valley, but they also gained France’s main possessions in the United States. This portion of land was basically the entire East coast to the Mississippi River. Because of this, I would say the answer is that the colonies lost territory.
Your final answer: B is your answer (The colonies lost territory).