Answer: c. both countries would fight until American independence was won.
The Treaty of Alliance (1778) was a defensive alliance between France and the US during the American Revolutionary War. In it, both parties agreed to fight together against the British if hostilities arose after the signing of the Treaty of Amity and Commerce.
The alliance was meant to last for an indefinite time in the future, and it was technically in effect until 1800. However, it was effectively broken when George Washington decided to remain neutral during the French Revolution.