Find the missing digit in the box. What is the missing digit?  $$\begin{matrix}\& \&~9~\&~\boxed{?}~\& 4 \textbackslash\textbackslash\& \times\& \& \&~6 \textbackslash\textbackslash{} \hline~\&5~\&~6~\& 0~\& 4\end{matrix}$$ 
选项为:A:$$0$$  B:$$5$$  C:$$3$$  D:$$4$$  请回答其中一个选项.