The countries in Group A have capitals that have two-word names. Respectively, the capitals are: Buenos Aires, Santo Domingo, Addis Ababa, Kuala Lumpur. Thus, Cambodia, whose capital is Phnom Penh, can be added to Group A. Respectively, the capitals of the remaining countries are: Paris, Athens, Oslo, Lisbon, Mogadishu.
Today's brain teaser courtesy of Braingle.com