Final answer:
The British surrendered at the Battle of Yorktown due to being surrounded by American and French forces, ending further military operations against the rebels. The European power that aided the colonists and ensured the surrender was France. Option d.
Step-by-step explanation:
The British surrendered at the Battle of Yorktown in 1781 because they were surrounded by over 9,500 American and 7,800 French forces led by General George Washington. This defeat made the outcome of the war all but certain and led to the end of further military operations against the rebels.
The European power that came to the aid of the colonists and ensured the British surrender was France. The French provided crucial military support, including troops, supplies, and naval blockade that cut off British support and forced the surrender of General Cornwallis at Yorktown.
So Option d is correct answer.