$x$ and $y$ are two correlated variables with the same standard deviation and the correlation coefficient $r$ , the correlation coefficient between $x$ and $x+y$ is

Question

$\begin {array} {1 1} (A)\;\large\frac{r}{2} & \quad (B)\;\sqrt{\large\frac{1-r}{2}} \\ (C)\;\sqrt{\large\frac{1+r}{2}} & \quad (D)\;0 \end {array}$