Beyond the answers - interesting background to this quiz

A peninsula with many neighbours

Serbia sits in the Balkans, the peninsula named after the Balkan Mountains that run through Bulgaria. The region is one of Europe's most complex cultural and linguistic mosaics, shaped by Roman, Byzantine, Ottoman and Austro-Hungarian rule at different times. That layered past is why the Balkans are often described as a crossroads between Europe and Asia Minor.

The shuttle that carried the Hubble telescope

Discovery was one of NASA's five operational Space Shuttle orbiters, alongside Columbia, Challenger, Atlantis and Endeavour. It flew more missions than any of its siblings, including the deployment of the Hubble Space Telescope in 1990 and the return-to-flight mission after the Challenger disaster. Its name followed a tradition of naming orbiters after famous exploring ships.

Carbon: the element that writes, burns and builds

Carbon's symbol is simply C, and it is the backbone of all known life. Its talent lies in bonding with itself and with other elements in almost endless arrangements, producing diamond, graphite and graphene from the same atoms. The symbol Ca, by contrast, belongs to calcium - a common source of confusion in chemistry exams.

The Gregorian calendar's quiet global takeover

The calendar introduced by Pope Gregory XIII in 1582 is now used for civil purposes in the vast majority of countries, well over 160 of them. Many nations that keep their own traditional calendars for religious or cultural life still rely on the Gregorian system for business, travel and government. Its leap-year rule is what keeps it aligned with the seasons.

When the Olympics became a political battlefield

The United States led a boycott of the 1980 Moscow Summer Olympics in protest against the Soviet invasion of Afghanistan. Dozens of countries stayed away, though some athletes competed under a neutral Olympic flag. Four years later, the Soviet Union and its allies returned the favour by boycotting the Los Angeles Games.