Beyond the answers - interesting background to this quiz

The mountain range that never sits still

The Tien Shan, whose name means "Mountains of Heaven" in Chinese, stretches roughly 2,500 kilometres across Central Asia, with its highest peaks in Kyrgyzstan and China. It is a young and active range, still being pushed upward as the Indian and Eurasian plates collide. That makes the region prone to powerful earthquakes, and it also feeds glaciers whose meltwater supplies rivers across a wide, dry region.

One small step, watched by millions

Apollo 11 landed on the Moon on 20 July 1969, and Neil Armstrong became the first person to walk on its surface. An estimated 600 million people watched the event on television, the largest live broadcast audience up to that time. The mission lasted about eight days in total, and the crew returned safely to Earth on 24 July.

Caesium, the element that defines the second

Caesium is a soft, golden-tinged metal that melts just above room temperature, and it reacts violently with water. Its most surprising role is in timekeeping: since 1967, the international definition of the second has been based on the vibration of caesium atoms. Atomic clocks built around this principle are accurate to within a second over millions of years.

Agatha Christie and the alphabet of murder

The ABC Murders, published in 1936, follows detective Hercule Poirot as he investigates a killer who appears to work through the alphabet, choosing victims whose names and locations match successive letters. Christie wrote more than 60 detective novels and remains one of the best-selling authors in history. The book is often cited as one of her cleverest plots.

Costa Rica and the many Costas

Costa Rica, meaning "rich coast", is a Central American country with coastlines on both the Pacific and the Caribbean. The other two options in this quiz are not countries at all: Costa de Almería and Costa Granadina are coastal regions of Spain, part of the country's long Mediterranean and Andalusian shoreline.