Your source is utterly incorrect. Tuvalu's highest point is 15ft (< 5 metres) above sea level, Kiribati and Palau are similar. In the Maldives, the highest point is just 7 feet (2 metres) above sea level. So what's the definition of a mountain? I didn't see one in the Vatican when I last visited and as it's so small it would be awfully hard to hide one. The quiz needs major correction IMO.