Beyond the answers - interesting background to this quiz

A story that aged backwards into fame

F. Scott Fitzgerald published "The Curious Case of Benjamin Button" in 1922, well before The Great Gatsby made him a household name. The story follows a man born old who grows steadily younger, and Fitzgerald reportedly drew the idea from a remark by Mark Twain about how life would be richer if it ran in reverse. The tale stayed relatively obscure for decades until a 2008 film adaptation brought it to a huge new audience.

The eye's clear window

The cornea is the transparent front layer of the eye, sitting over the iris and pupil like a curved windshield. It has no blood vessels, which helps keep it clear, and it does much of the eye's focusing work. Because it is so exposed, it also depends on tears and blinking to stay moist and free of grit.

A mirror, a dog and a mystery

Jan van Eyck's "The Arnolfini Portrait", painted in 1434, is one of the most scrutinised pictures in Western art. At its centre hangs a round convex mirror, and in it you can see tiny reflections of two figures standing in the doorway. The painting is packed with possible symbols - a small dog, discarded shoes, a single lit candle - whose meanings scholars still debate.

The river between two civilisations

The Tigris rises in the mountains of eastern Turkey and flows through Iraq before joining the Euphrates and emptying into the Persian Gulf. Along with the Euphrates, it defined Mesopotamia, the "land between the rivers", where some of the world's earliest cities and writing systems emerged. Its waters remain a lifeline for millions of people today.

When the world's economy stalled

The Great Depression began with the Wall Street Crash of 1929 and gripped much of the world through the 1930s. Banks failed, international trade collapsed and unemployment reached staggering levels in countries such as the United States and Germany. Its shadow shaped economic policy and politics for generations afterwards.