Decrete math question But it is quiet confusing Can anyone explain the question?

Question

For the domain predicate D,
a.D(if B then S1 else S2 fi) ⇔ D(B) ∧ (D(S1) ∨ D(S2)
b.D(S1; S2) = D(D(S1)) ∧ D(S2)
c.D(if B then S1 fi) ⇔ (B → D(S1)) ∨ (¬B → D(S2))
d.D