Question

The intergovernmental military alliance to which the United States, Canada, and Britain belong is called __________.

Answer 1

NATO. Stands for North Atlantic Treaty Organisation. The military alliance between them all. I actually learned this last week. 

Answer 2

A) incorrect, NAFTA is a North American free trade agreement which has nothing to do with the UK
B) incorrect, the US and Canada aren't in the EU
C) correct
D) incorrect, that's a Union of south american nations


TL;DR = C is the correct answer :)