A giant map of European countries at the E.U. Commission in Brussels, Belgium.   (Julien Warnand/EPA)

Later this month, Britain will vote on leaving the European Union. If British voters decide they really want to leave, it will be a big event. No country has ever decided to leave the modern E.U. The consequences for Britain, let alone the E.U., are unclear.

Many non-Europeans may struggle to see what the fuss is about. In fact, many might scratch their heads and wonder what exactly the E.U. does and how it relates to European country-level governments.

This isn't just a problem for those outside of the E.U.'s boundaries, however. In "Brexit: The Movie," people on the street in both London and Brussels were shown photographs of extremely important leaders and asked who they are. It appears everyone is stumped. The film may have a clear political angle, but it does make a key point: To many European citizens, the institution that controls many aspects of their lives is a mysterious and opaque mess.

So what do you actually know about one of the most important political institutions in the world? Take our test and find out.

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