For a heterogeneous catalytic reaction, A + B → C, with equimole feed of A and B, the initial rate – rA0 is invariant with total pressure. The rate controlling step is______________________?

A. Surface Kc/(1 + TS) reaction between absorbed A and B in the gas phase
B. Surface reaction between absorbed A and absorbed B
C. Surface reaction between A in the gas phase and absorbed B
D. Desorption of C