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Spherical rain drop evaporates at a rate...

Spherical rain drop evaporates at a rate proportional to its surface area. The differential equation corresponding to the rate of change of the radius of the rain drop if the constant of proportionality is `K >0` is

A

A) `(dr)/(dt)+k=0`

B

B) `(dr)/(dt)-k=0`

C

C) `(dr)/(dt)-kr`

D

D) None of these

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