What is the auto correlation of the sequence x(n)=anu(n), 0<a<l?

• A. ( frac{1}{1-a^2} ) a^l (l 0)
• B. ( frac{1}{1-a^2} ) a^-l (l&lt;0)
• C. ( frac{1}{1-a^2} ) a^|l|(- &lt;l&lt; )
• D. All of the mentioned