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Multiple data.tables, multiple keys

Three new data.tables are available in your workspace: area, capitals, and population, containing basic statistics about the geography and demographics of Australia.

Which columns can be used to match rows across these three data.tables?

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None, because no column is present in all three data.tables.

The "state" column in area and capitals. But no key can uniquely identify rows in population and capitals.

The "state" column for joining area and capitals, and the "city" column for capitals and population.

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