World War I only officially ended in 1990.
Why it is true
Although fighting ceased in 1918, the definitive peace treaty with Germany was only signed in 1990 after the country's reunification.
Source: History
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.