Two $2^{\prime}$ 's complement number having sign bits $x$ and $y$ are added and the sign bit of the result is $z$. Then, the occurrence of overflow is indicated by the Boolean function
- $x y z$
- $\bar{x} \bar{y} \bar{z}$
- $\bar{x} \bar{y} z+x y \bar{z}$
- $x y+y z+z x$