4. If $x+\frac{1}{y}=1, y+\frac{1}{z}=1$, then the value of $x y z$ is ( ).
(A) 1
(B) -1
(C) $\pm 1$
(J) $\pm 2$
4. (13).

From $1 \frac{1}{y}=1$ we get $x y=y-1$.
From $y \frac{1}{z}=1$ we get $\quad y z=z-1$.
$$
\begin{array}{l}
\quad \mathrm{L}, x y=\frac{(y-1)(z-1)}{y} . \\
x \frac{1}{y}=1-x, y-1=-\frac{1}{z} ; \text { substituting into the above, we get } \\
x y z=-1 .
\end{array}
$$