$1=\{$ a$,$ b$\}$ and S$2=\{$b$,$ c$\}.$ which one is NOT in S$1$ x S$2?$

A$)($a$,$ a$)$

B$)($b$,$ c$)$

C$)($a$,$ b$)$

D$)($b$,$ b$)$