In a math competition, each participant has a unique $5$-digit registration number of the form $\overline{BBCAC}$, where $0 \leq A \textless{} B\textless{} C \leq 9$ and $B$ is the average of $A$ and $C$. What is the maximum number of participant that can join this competition? 
选项为:A:$$12$$  B:$$16$$  C:$$18$$  D:$$20$$  E:$$25$$  请回答其中一个选项.