One classical breakdown of economic activity distinguishes three sectors :
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1-587: In the 20th century, economists began to suggest that traditional tertiary services could be further distinguished from " quaternary " and quinary service sectors. Economic activity in the hypothetical quaternary sector comprises information- and knowledge-based services, while quinary services include industries related to human services and hospitality . Economic theories divide economic sectors further into economic industries . An economy may include several sectors that evolved in successive phases: Even in modern times, developing countries tend to rely more on
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