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This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

The population of Paris today is lower than its historical peak of 2.9 million in 1921. The principal reasons were a significant decline in household size, and a dramatic migration of residents to the suburbs between 1962 and 1975. Factors in the migration included de-industrialisation, high rent, the gentrification of many inner quarters, the transformation of living space into offices, and greater affluence among working families. The city's population loss came to an end in the 21st century; the population estimate of July 2004 showed a population increase for the first time since 1954, and the population reached 2,234,000 by 2009.
Output:
What is Paris' peak population?