A student reads a passage arguing that urban green spaces reduce stress. The author cites a study showing lower cortisol levels in city residents who visit parks weekly. What is the primary purpose of including this study?
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A
To entertain readers with anecdotes about park visitors
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B
To provide empirical support for the claim about stress reduction
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C
To compare urban and rural cortisol levels
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D
To explain how cortisol is measured in laboratory settings