Beyond the answers - interesting background to this quiz

A pandemic that circled a wartime world

The Spanish flu pandemic of 1918-1919 is the event from this quiz that belongs to the 20th century, and it remains one of the deadliest outbreaks in recorded history. It spread during the final months of the First World War, helped along by troop movements and crowded conditions. The name is misleading: the illness did not originate in Spain, but Spanish newspapers, neutral in the war, reported on it more freely than censored press elsewhere.

One river, two countries, many states

The Columbia River rises in the Canadian province of British Columbia and flows through just two states, Washington and Oregon, before reaching the Pacific Ocean. Its drainage basin, however, is far larger, touching parts of several other states and provinces. The river is central to the Pacific Northwest, shaping trade, hydropower and salmon runs that have sustained Indigenous communities for thousands of years.

Tin and the mystery of Sn

Tin's chemical symbol, Sn, comes from the Latin word stannum. That can puzzle anyone expecting the letters to match the English name, as they do for titanium (Ti). Tin has been used for millennia, notably alloyed with copper to make bronze, a material so important that it gave its name to an entire age of human history.

Brazil and its many neighbours

Brazil borders ten countries, which is more than any other nation in South America. Its neighbours include Argentina, Bolivia, Colombia, Peru and Venezuela, among others. The only South American countries it does not border are Chile and Ecuador. That long land frontier helps explain Brazil's size and its role as a regional power.

The Sahel, a belt of transition

Burkina Faso sits within the Sahel, the semi-arid band that stretches across Africa between the Sahara to the north and wetter savannas to the south. The name comes from the Arabic word for "coast" or "shore", reflecting how the region was once imagined as the edge of the desert. Countries across the Sahel share challenges such as drought, food security and rapid population growth.