$\mathrm{AgNO}{}_3$ is added gradually to a solution containing $0.010\mathrm{M}$ each of $\mathrm{Cl}{}^{-}$, $\mathrm{Br}{}^{-}$ and $\mathrm{I}{}^{-}$. $K_{sp}$: $\mathrm{AgCl}=1.8\times 10^{-10}$, $\mathrm{AgBr}=5.0\times 10^{-13}$, $\mathrm{AgI}=8.0\times 10^{-17}$. Choose the correct statement(s).

1. A$\mathrm{AgI}$ is the first to precipitate
2. B$\mathrm{AgCl}$ begins to precipitate at $[\mathrm{Ag}{}^{+}]=1.8\times 10^{-10}\mathrm{M}$
3. CWhen $\mathrm{AgBr}$ just begins to precipitate, $[\mathrm{I}{}^{-}]$ left is $1.6\times 10^{-6}$ $\mathrm{M}$
4. D$\mathrm{AgBr}$ precipitates before $\mathrm{AgI}$