Cho log a x =p, log b x =q, log abc x =r. Hãy tính log c x theo p, q, r

A. ${\log }_{c}x=\frac{1}{r}-\frac{1}{p}-\frac{1}{q}$

B. ${\log }_{c}x=\frac{1}{\frac{1}{r}+\frac{1}{p}+\frac{1}{q}}$

C. ${\log }_{c}x=\frac{1}{\frac{1}{r}-\frac{1}{p}-\frac{1}{q}}$

D. ${\log }_{c}x=\frac{1}{r}+\frac{1}{p}+\frac{1}{q}$