A reaction $\mathrm{A}\rightleftharpoons \mathrm{I}\to \mathrm{P}$ has rate constants $k_1=2.0\times 10^{-3}{\mathrm{s}}^{-1}$ (A to I), $k_{-1}=30{\mathrm{s}}^{-1}$ (I to A) and $k_2=20{\mathrm{s}}^{-1}$ (I to P). Applying the steady-state approximation to the reactive intermediate I, the effective first-order rate constant for the disappearance of A is

1. A$2.0\times 10^{-3}{\mathrm{s}}^{-1}$
2. B$1.3\times 10^{-3}{\mathrm{s}}^{-1}$
3. C$1.2\times 10^{-3}{\mathrm{s}}^{-1}$
4. D$8.0\times 10^{-4}{\mathrm{s}}^{-1}$