Observe that each number is the sum of the number of previous term and the difference between adjacent numbers. 
In the arithmetic sequence $5$, $7$, $9$, $11$ $\cdots$ , the $9$\textsuperscript{th} term is~\uline{~~~~~~~~~~}~. 

1. $$19$$ 
2. $$21$$ 
3. $$23$$ 
4. $$25$$ 