In the following reaction,

$\underset{\text{ Acid }}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}+\underset{\mathrm{X}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\underset{ }{\rightleftharpoons } \underset{\mathrm{conjugate} \mathrm{acid}}{ {\mathrm{H}}_3{\mathrm{O}}^{+}}\left(\mathrm{aq}\right)+\underset{\mathrm{Y}}{{\mathrm{OH}}^{-}}\left(\mathrm{aq}\right)$

X and Y respectively are

• A

  base and conjugate acid

• B

  acid and conjugate base

• C

  base and conjugate base

• D

  acid and conjugate acid