Beyond the answers - interesting background to this quiz

A river that has shaped more than one country

The Rhine rises in the Swiss Alps and flows through several countries before reaching the North Sea, with Germany among them. For centuries it has served as a major trade route, and its banks are lined with castles, vineyards and industrial cities. It also forms part of the border between Germany and France, which is why the river appears in the history of both countries.

The planet that rolls rather than spins

Uranus has an axial tilt of roughly 98 degrees, meaning it effectively rotates on its side. This extreme tilt gives the planet some of the strangest seasons in the solar system, with each pole facing the Sun for about 42 Earth years at a time. Its moons and faint rings follow the same tilted plane, making the whole system look unlike any other planet's.

Why 2 is the odd one out among primes

A prime number has exactly two factors: one and itself. The number 2 fits this definition, but it is also the only even prime, since every other even number can be divided by 2. That single exception makes 2 a frequent trap in maths questions, and it is also the starting point for many proofs about how primes behave.

The Black Sea and its crowded shoreline

The Black Sea is bordered by six countries: Bulgaria, Romania, Ukraine, Russia, Georgia and Turkey. This makes it a meeting point between Europe and Asia, and its ports have long been important for trade in grain, oil and goods. Because several of those countries have changed borders over the past century, the sea's political map looks quite different today than it did a hundred years ago.