The correct answer is A. The battle that is considered a turning point un the War of Independence is the Siege of Yorktown.
The Siege of Yorktown took place during the War of Independence of the United States of America between September 26 and October 19, 1781. It faced the Continental Army and their French allies against the British forces led by Lord Cornwallis, with the revolutionary side winning it.
The Siege of Yorktown was of decisive importance for the outcome of the War of Independence and led the British government to undertake peace negotiations with the United States.