$($a$)$ Three parallel liquid phase reactions with corresponding rate laws are given below for one desired $D,$ and two undesired products, $U_1$ and $U_2.$ How and under what conditions $($reactor type and concentration$)$ should the reaction be carried out to maximize the selectivity of $D?$

$A+BD,r_D=k_1{C}_A^2{C}_B,k_1=0\mathrm{.}0075mo{l}^{-2}{L}^2{s}^{-1}$

$A+B{U}_1,r_{U1}=k_2{C}_A{C}_B,k_2=0\mathrm{.}0084mo{l}^{-1}L{s}^{-1}$

$A+B{U}_2,r_{U2}=k_3{C}_A^3{C}_B,k_3=0\mathrm{.}016mo{l}^{-3}{L}^3{s}^{-1}$