Immobilized Enzyme - Medical Science

Q1:

If Damkohler number, NDa >>1, the reaction rate is much greater than the mass transfer rate and the overall reaction is controlled by the rate of mass transfer. In this case, the enzyme reaction can be described as (where Csb and Cs are the substrate concentration in bulk of solution and at the immobilized enzyme surface respectively. ks mass transfer coefficient, and a is the surface area of an immobilized enzyme particles)

A rp = ksa(Csb-Cs)

B rp = ksaCsb

C rp = ksaCs

D rp = ksa(Csb+Cs)

ANS:B - rp = ksaCsb

Please explain the answer in detail to understand.