Review the equilibrium and choose the correct statement:
$HClO_4 + H_2O \rightleftharpoons H_3O^{+} + ClO_4^-$

• A
  $HClO_4$ is the conjugate acid of $H_2O$
• B
  $H_3O^{+}$ is the conjugate base of $H_2O$
• C
  $H_2O$ is the conjugate acid of $H_3O^{+}$
• D
  $ClO_4^-$ is the conjugate base of $HClO_4$