Write a recursive formula for the geometric sequence $\left\lbrace18,6,2,\frac23,\ldots\right\rbrace$.

• A. $a_{n}=3a_{n-1}$
• B. $a_{n}=\frac{a_{n-1}}{3}$
• C. $a_{n}=18a_{n-1}$
• D. $a_{n}=\frac23a_{n-1}$