Which of the following rate laws suggests that the reaction probably occurs in a single step?

why is this problem cant be answer a since it has order of 1

a)(CH3)3CBr + OH- →(CH3)3COH + Br- rate = k[(CH3)3CBr]

b)NO(g) + O2(g) → NO2(g) + O(g) rate = k[NO][O2]

c)H2O2 + 3 I- + 2 H+→ I3- +2H2O
rate= kl[H2O2][I-]+K2[H2O2][I-][H+]

d)H2(g) + Br2(g) → 2 HBr(g)
rate = k[H2][Br2]1/2