i need explanation please

Knowing that the selectivity is given by Soyu = (k1/k2) Cp/CA. the reactor that will increase formation of D is a. CSTR reactors in series where A is split and fed to each reactor and B is fed once to the first reactor b. None C. CSTR reactors in series where B is split and fed to each reactor and A is fed once to the first reactor d. A membrane reactor where B is fed into side streams to the reactor and A is fed once to the first reactor Knowing that the selectivity is given by: Spru = (k1/k2) CA/Cg, the reactor that will increase the formation of Dis Select one: a. CSTR reactors in series where B and A are fed together to the first reactor b. CSTR reactors in series where B is split and fed to each reactor and A is fed once to the first reactor c. None d. CSTR reactors in series where A is split and fed to each reactor and B is fed once to the first reactor