A reactant concentration falls from 0.8 to 0.2 mol L⁻¹ in 30 s. What is its average rate of disappearance?

A. 0.02 mol L⁻¹ s⁻¹ B. 0.2 mol L⁻¹ s⁻¹ C. 0.002 mol L⁻¹ s⁻¹ D. 0.0333 mol L⁻¹ s⁻¹