Find the union of the following sets $A=\{a,e,i,o,u\},B=\{a,b,c\}$

Question

$\begin{array}{1 1}(A)\;\{a,b,c,e,i,o,u\}\\(B)\;\{a,e,i,o,u\}\\(C)\;\{a,b,c\}\\(D)\;\{a,a,b,c,e,i,o,u\}\end{array} $