Definition: Generate a question which can yield the answer mentioned in the input. Generated question must be answered by the answer provided in input, without using any extra knowledge.
Input: Context : The 2007 enlargement of the European Union saw Bulgaria and Romania join the European Union (EU) on 1 January 2007.
Answer : 1 January 2007
Output:
On what date did 2007 enlargement of the European Union occur?