An amphoteric substance is one that can act as both an acid and a base.

An amphoteric substance is one that can act as both an acid and a base.

Let's examine each option:

• A- $\text{HCO}_3^{-}$ (Bicarbonate ion):

  • Can act as an acid by donating a proton: $\text{HCO}_3^{-} \rightleftharpoons \text{CO}_3^{2-} + \text{H}^{+}$
  • Can act as a base by accepting a proton: $\text{HCO}_3^{-} + \text{H}^{+} \rightleftharpoons \text{H}_2\text{CO}_3$
  • Thus, $\text{HCO}_3^{-}$ is amphoteric.

• B- $\text{NH}_3$ (Ammonia):

  • Can act as an acid by donating a proton (e.g., in reactions with very strong bases or in autoionization): $\text{NH}_3 \rightleftharpoons \text{NH}_2^{-} + \text{H}^{+}$
  • Can act as a base by accepting a proton: $\text{NH}_3 + \text{H}^{+} \rightleftharpoons \text{NH}_4^{+}$
  • Thus, $\text{NH}_3$ is amphoteric.

• C- $\text{H}_2\text{O}$ (Water):

  • Can act as an acid by donating a proton: $\text{H}_2\text{O} \rightleftharpoons \text{OH}^{-} + \text{H}^{+}$
  • Can act as a base by accepting a proton: $\text{H}_2\text{O} + \text{H}^{+} \rightleftharpoons \text{H}_3\text{O}^{+}$
  • Thus, $\text{H}_2\text{O}$ is amphoteric.

Since all three substances ($\text{HCO}_3^{-}$, $\text{NH}_3$, and $\text{H}_2\text{O}$) exhibit amphoteric behavior, the correct option is D.

The final answer is $\boxed{\text{D- All of the above}}$.