[university probability theory] set theory

this is the problem: For each of the following statements, decide whether they are always true (i.e., true for all sets A, B, C) or not. If they are not always true, provide a counter example for instance in the form of a Venn Diagram or by listing specific sets. (a) If A ∪ B = A, then B ⊂ A. (b) If A ⊂ B, then A ∪ B = A. i think that the first one is always true, but the second one isn't. but i am not sure how to explain why.