In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.

Let me give you an example: This list contains the top 25 accounts with the most followers on the social photo-sharing platform Instagram. As of May 2018, the most followed user is Instagram's own account, with over 235 million followers. Selena Gomez is the most followed individual, with over 137 million followers. Ten accounts have exceeded 100 million followers on the site.
The answer to this example can be: who has the maximum number of followers on instagram
Here is why: The answer is talking about the Instagram accounts that have the most followers. The question asking about the maximum number of followers. So this is a good example.

OK. solve this:
The disaster began during a systems test on 26 April 1986 at reactor 4 of the Chernobyl plant near Pripyat and in proximity to the administrative border with Belarus and the Dnieper River. There was a sudden and unexpected power surge. When an emergency shutdown was attempted, a much larger spike in power output occurred. The second spike led to a reactor vessel rupture and a series of steam explosions. These events exposed the graphite moderator of the reactor to air, causing it to ignite. The resulting fire sent week long plumes of highly radioactive fallout into the atmosphere over an extensive geographical area, including Pripyat. The plumes drifted over large parts of the western Soviet Union and Europe. According to official post-Soviet data, about 60% of the fallout landed in Belarus.
Answer:
what caused the nuclear disaster in chernobyl ukraine