A Buffer Pair (HA/A $\left.\mathrm{A}^{-}\right)$ Has A $\mathrm{pK}$ Of 54 at a Blood

A buffer pair (HA/A $\left.\mathrm{A}^{-}\right)$ has a $\mathrm{pK}$ of 5.4. At a blood $\mathrm{pH}$ of 7.4, the concentration of HA is

A) $1 / 100$ that of $\mathrm{A}^{-}$
B) $1 / 10$ that of $\mathrm{A}^{-}$
C) equal to that of $\mathrm{A}^{-}$
D) 10 times that of $\mathrm{A}^{-}$
E) 100 times that of $\mathrm{A}^{-}$