Let A, B, and C be sets. Show that

Let A, B, and C be sets. Show that

a) (A ∪ B) ⊆ (A ∪ B ∪ C).
b) (A ∩ B ∩ C) ⊆ (A ∩ B).
c) (A − B) − C ⊆ A − C.
d) (A − C) ∩ (C − B) = ∅.
e) (B − A) ∪ (C − A) = (B ∪ C) − A.