You didn't provide a list of choices, so I'll simply list some of the major international associations in which the United States is a participating member:
- The United Nations (UN)
- The North Atlantic Treaty Organization (NTO)
- The World Trade Organization (WTO)
- The International Monetary Fund (IMF)
- The Group of Seven (G7) -- which used to be the G8 until Russia was suspended because of its invasion of Crimea. The G7 consists of the nations with the largest advanced economies in the world (Canada, France, Germany, Italy, Japan, the United Kingdom, and the United States).
- The World Health Organization (WHO)
- The International Olympic Committee (IOC)
There are lots of others, but those are some of the major international organizations or groups to which the US belongs.