Identify the conjugate acid and conjugate base respectively in the following reaction:
$H_2O + HCl_{(aq)} \leftrightharpoons H_3O^{+} + Cl_{(aq)}^{-}$

• A
  $H_2O$ and $H_3O^{+}$
• B
  $H_3O^{+}$ and $H_2O$
• C
  $Cl^{-}$ and $HCl$
• D
  $H_3O^{+}$ and $Cl^{-}$