For sure, Baz...Karen Carpenter!!!
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Patsy Cline
Minimally, in the top 10 of all time.
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Sarah Brightman
She has an astonishing ability to adapt her voice to sing (brilliantly) in any musical style or genre - pop, rock, opera, etc.
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Aretha Franklin
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Enya
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My sister, Shirley Pearson
A recorded artist who sings pop and opera...anything, really.
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Edit: And yes, Tracy Chapman