Which of these numbers are prime numbers?  $2\textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} 6\textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} 7\textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} 9\textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} 12\textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} \textbackslash{} 15$ 
选项为:A:$2$ and $9$  B:$6$ and $7$  C:$9$ and $15$  D:$2$ and $7$  请回答其中一个选项.