Which of the following is true?

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(C) Using the sine rule,we have $a = 2R\sin A$,$b = 2R\sin B$,and $c = 2R\sin C$.Substituting these into the expression:$a\cos A + b\cos B + c\cos C =

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$a\cos A + b\cos B + c\cos C = 4R\sin A\sin B\sin C$

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(C) Using the sine rule,we have $a = 2R\sin A$,$b = 2R\sin B$,and $c = 2R\sin C$.Substituting these into the expression:$a\cos A + b\cos B + c\cos C = (2R\sin A)\cos A + (2R\sin B)\cos B + (2R\sin C)\cos C$$= R(2\sin A\cos A + 2\sin B\cos B + 2\sin C\cos C)$$= R(\sin 2A + \sin 2B + \sin 2C)$Using the identity $\sin 2A + \sin 2B + \sin 2C = 4\sin A\sin B\sin C$ for a triangle $ABC$:$= R(4\sin A\sin B\sin C)$$= 4R\sin A\sin B\sin C$.

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