Under Certain Conditions the Reaction H₂O₂ + 3I^- + 2H⁺ $\to$

Under certain conditions the reaction H₂O₂ + 3I^- + 2H⁺ $\to$ I₃^- + 2H₂O occurs by the following series of steps:
k₁
Step 1.
H₂O₂ + H⁺ H₃O₂⁺
k_-1 Step 2.
H₃O₂⁺ + I^- $\to$ H₂O + HOI
(slow,rate constant k₂)
Step 3.
HOI + I^- $\to$ OH^- + I₂
(fast,rate constant k₃)
Step 4.
OH^- + H⁺ $\to$ H₂O
(fast,rate constant k₄)
Step 5.
I₂ + I^- $\to$ I₃^-
(fast,rate constant k₅)
-Which of the steps would be called the rate-determining step?

A) 1
B) 2
C) 3
D) 4
E) 5