Why could cornwallis not be reinforced by british ships coming down the york river from the west

This event happened during the Siege of Yorktown, that was a battle that happened in Yorktown - Virginia between American and French Army and British Army. Charles Cornwallis was the Lieutenant General of the British Army and he surrendered because of the capture of him and his army.

The ships of Britain could not help him because the French army - that was on American’s side - were firing on them. Another French ship prevented them from escaping to the sea.

is there multiple choice or do you need like an essay answer?