12.設\( f(x) = 3^x \), \( g(x) = \log_{\frac{1}{3}} x \)，則下列選項何者正確？
(A)若x₁<x₂，則\( 3^{x_1} > 3^{x_2} \)
(B)若x₁<x₂，則\( 3^{x_1} + 3^{x_2} = 3^{x_1+x_2} \)
(C)若x₁<x₂，則\( \log_{\frac{1}{3}}(x_2 - x_1) = \log_{\frac{1}{3}} x_2 - \log_{\frac{1}{3}} x_1 \)
(D)若x₁<x₂，則\( \frac{\log_{\frac{1}{3}} x_2 - \log_{\frac{1}{3}} x_1}{x_2 - x_1} < 0 \)

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