For a reaction taking place in three steps, the rate constants are `k_1, k_2` and `k_3`. The overall rate constant `k= (k_1 k_2)/k_3` . If the energy of activation values for the first, second and third stages are respectively 40, 50 and 60 kJ `mol^-1`, then the overall energy of activation in kJ `mol^-1` is

Options

A. 30
B. 40
C. 60
D. 50