Final answer:
France was the European country that aided the American colonists during the Revolutionary War, as evidenced by the Treaty of Alliance from 1778.
Step-by-step explanation:
The European country that sided with the American colonists and aided them in the Revolution was France. Option C from the first question provided is the correct answer, making the selection from the multiple-choice answers, answer c. C only. France's support was crucial to the American victory in the Revolutionary War, as they provided military aid and resources to the colonists. This is highlighted by the Treaty of Alliance from 1778, where France agreed to offer military support to the United States against Great Britain, which was engaged in several conflicts with France, including the French and Indian War where Great Britain was against the French and their Native American allies. Additionally, Germany did provide soldiers to the British side as mercenaries, commonly known as Hessians, but as a country did not officially aid the American colonists.