I believe it the third choice (C.) they were inspired by the American struggle for liberty.
Because:
At first France’s defeat to Britain in the Seven Years War motivated them to join the Americans in the fight against Britain. At the beginning of the war the Europeans(France) gave loans and other assistance through a American trader his name was Silas Deanne. But once the Americans won the victory at the Battle of Saratoga in 1777 France soon became convinced that the American cause was worthy. So France and the Americans signed the Treaty of Amity and Commerce on February 6,1778,and France then formally joined the war with the Americans