Given the following sets.

a = {0, 1, 2, 3}
b = {a, b, c, d}
c = {0, a, 2, b}

find b∪c

1. {0, 1, 2, 3}
2. {a, b, c, d}
3. {0, a, 2, b}
4. {a, b, c, d, 0, 2}
5. empty set