The general rule is that the pK1 or a dicarboxylic acid is lower (more acidic) than the pKa of a regular carboxylic acid, and the pK2 is a little higher (less acidic).
Why is this? Because carboxylic acids are electron withdrawing groups (EWG). They stabilize the conjugate base of an acid, making the acid more acidic. So Both D and A should be more acidic than C. Because A has its carboxylic acid groups closer together, the EWG effect is stronger, and it will be the most acidic.
B will be the least acidic of the group. Why? Because a carboxylate group has a negative charge, which is electron donating and destablizing to the conjugate base (is a molecule is already -1, it doesn't help to become -2.)
So the overall order is:
(strongest acid) A > D > C > B (weakest acid)
