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LONDON — The 75-year-old American professor had lived in the Swiss town of Einsiedeln for nearly 40 years when he decided to take a citizenship test to acquire a Swiss passport. The unnamed man spoke fluent German and had few reasons to believe that anyone could have objections to him being eligible for a Swiss passport, local media reported in 2014.

Yet the professor — who teaches at the world-class university ETH Zurich, where Albert Einstein received his diploma — was refused citizenship.

He had failed a multiple-choice test.

Critics of Europe's citizenship tests have pointed out that they do not follow a common pattern or they are based on little research as to what questions are needed to distinguish migrants who are willing to assimilate from those who are not. And yet, they have the potential to determine the fate of thousands. Particularly amid the recent influx of migrants into Europe, there has been a renewed focus on a contentious question: How should a test that will help determine whether an individual can acquire citizenship look?

In Denmark, it looks like this:

"Which Danish restaurant gained a third Michelin star in February 2016?"

Many of the questions in Denmark's new citizenship test have been criticized as unnecessarily tough or out of touch with the reality of everyday life. After the country revamped its questions to make the test harder, nearly 70 percent of all June applicants failed.

Danish newspapers suggested that many citizens would have failed it, too. Opponents of the Danish government immediately alleged that the tougher citizenship questions were part of an effort to discourage refugees from choosing to come to the country. The Nordic country had recently imposed a series of immigration restrictions.

Integration Minister Inger Stojberg defended the measures in an interview with Danish newspaper Politiken, saying "citizenship is something you have to earn."

Doubts over such governmental defenses have not only been voiced in Denmark, but also in other nations such as Britain.

There, more than half the country's citizens age 18 to 24 would fail the citizenship test, a YouGov poll suggested two years ago.

Writing in British newspaper the Chronicle, Durham University professor Thom Brooks argued in June that the "citizenship exam has become a test of the purely trivial." Handbooks that are supposed to prepare test-takers feature 3,000 facts and more than 250 dates to be memorized.

"Native-born citizens expressed surprise — sometimes horror — about what the test asks in their name," Brooks wrote, reflecting on interviews he had recently conducted with British citizens. According to the migration researcher and columnist, European governments have long underestimated the discouraging repercussions of the citizenship tests currently in place.

"The effect of making many new citizens pass knowledge tests that no born British citizen could runs the serious risk of not bringing future British citizens together, but helping push them apart," Brooks argued.

Could you become a citizen of these three European countries?

Many E.U. countries require foreigners to pass tests if they want to become citizens. To give you an idea of why these tests have been criticized for being too tough, here are some sample questions from various nations. (Can't see the quiz? Click here.)