9 Given $z \in \mathbf{C}$, and $\arg z=\theta$, then the principal value of the argument of the complex number represented by the point symmetric to $i \bar{z}$ with respect to the line $y=x$ is
A. $\pi-\theta$
B. $2 \pi-\theta$
C. $\frac{\pi}{2}+\theta$
D. $\theta$
9 D. Let $z=a+bi$, then $\bar{z}=a-bi, i\bar{z}=b+ai, i\bar{z}$ is the reflection of the point representing the complex number $a+bi$ (i.e., $z$) over the line $y=x$.