Let $A=\{a,b\},B=\{a,b,c\}$.Is $A\subset B$?What is $A\cup B$?

Question

$\begin{array}{1 1}(A)\;No,\{a,b,c\}&(B)\;Yes,\{a,b\}\\(C)\;Yes,\{a,b,c\}&(D)\;No,\{b,c\}\end{array} $