(b) USA
The USA is an example of a 'coming together' federation, where independent states voluntarily joined to form a union.
CBSE distinguishes between two types of federation: 'coming together' (independent states unite — e.g., USA, Australia, Switzerland) and 'holding together' (a large country divides power to keep the nation united — e.g., India, Belgium, Spain). India and Spain are 'holding together' federations; Belgium uses a unique community government model but is also a 'holding together' type. The USA is the classic textbook example of 'coming together.' Source: Federalism, Chapter 2, Democratic Politics.