-What Is the Norton Equivalent Impedance Zn External to ZL $\Omega \angle$

-What is the Norton equivalent impedance Zn external to ZL?

A) 10.0 $\Omega \angle$
0°
B) 5.0 $\Omega \angle$
90°
C) 0.47 $\Omega \angle$
-26.6°
D) 11.2 $\Omega \angle$
26.6°