Consider the following countries:
I. Austria
II. Bulgaria
III. Croatia
IV. Serbia
V. Sweden
VI. North Macedonia
How many of the above are members of the North Atlantic Treaty Organization?

Correct Option: Only four

Let us evaluate the membership of the North Atlantic Treaty Organization (NATO): Austria is a neutral country and not a NATO member. Bulgaria joined NATO in 2004. Croatia joined in 2009. Serbia is not a NATO member and maintains military neutrality. Sweden officially joined NATO in 2024, making it a member. North Macedonia joined NATO in 2020. Out of the six listed countries, Bulgaria, Croatia, Sweden, and North Macedonia (total four countries) are members of NATO, while Austria and Serbia are not. Therefore, the correct option is 'Only four'.