L1' - L2 = L1' ∩ L2' = CSL ∩ Recursive = Recursive ∩ Recursive = Recursive
Points to be noted: CSL are closed under complementation. Complementation of CFL is Recursive and every CSL is recursive.
B . L1 - L2' = CSL - Rec = CSL ∩ Rec = Recursive ∩ Recursive = Recursive
C. L1 ∩ Regular is not equal to Regular, consider $\sum$ = {a,b} regular language be (a+b)* and csl be anbn , then there intersection is anbn which is not regular.
D. L1.L2 = CSL.CFL = CSL because every cfl is csl and csl are closed under concatenation. for concatenation of CSL and CFL, let's say CSL be anbncn and CFL be am , concatenation will be anbncnam but how will you check anbncn using PDA as it not context free. Hence D is true