L1 = {$a^nb^n, n >=0$}, L2 =$ (a+b)^*$, L2' = { }
A. $L1 - L2 = L1 ⋂ L2'$
$L1 ⋂ L2' = ${ }
Which is CFL. So A is false as it can can be CFL.
B. Intersection of CFL and RL is CFL always. So B is correct.
C. CFL isn't closed under complement. So C is false.
So D is correct.