The correct answer is A) The French fleet arrived at the right moment to blockade a British escape.
The American victory at Yorktown can be called "lucky" in that the French fleet arrived at the right moment to blockade a British escape.
On October 19, 1781, and with the help of the Frenchs, the American army defeated the British troops that were trapped at Yorktown, Virginia. This victory represented the culmination of the American Revolution and the American colonies gained independence from Great Britain. On September 3, 1783, the United States and England signed the Treaty of Paris, accepting the independence of the US.