If $a_{1}=0$ and $a_{1}, a_{2}, a_{3}, \ldots, a_{n}$ are real numbers such that $\left|a_{i}\right|=\left|a_{i-1}+1\right|$ for all $i$ then the A.M. of the numbers $a_{1}, a_{2}, \ldots, a_{n}$ has value $x$ where
(A) $x \leq-\frac{1}{2}$
(B) $x \geq-\frac{1}{2}$
(C) $x<-\frac{1}{2}$
(D) None of these