Given three sets X={a,b}X = \{a, b\}X={a,b}, Y={b,c}Y = \{b, c\}Y={b,c}, and Z={c,d}Z = \{c, d\}Z={c,d}, what is the union X∪Y∪ZX \cup Y \cup ZX∪Y∪Z?
{b,c}\{b, c\}{b,c}
{a,b,c,d}\{a, b, c, d\}{a,b,c,d}
{a,b,b,c,c,d}\{a, b, b, c, c, d\}{a,b,b,c,c,d}
∅\emptyset∅