Answer:
C. A Treaty
Explanation:
A treaty is a binding agreement that is made between parties through a negotiation process. It, therefore, a form of a contract that is signed or passed formally based on its nature. It established an obligation between two parties.
Having understood that, the given example is a treaty because parties have arrived into an agreement to save their money for buying their parents anniversary gifts. Through their negotiation, they arrived at a mutual understanding of what they wanted to buy.
