2. If $x=\frac{-1+\sqrt{3} \mathrm{i}}{2}, y=\frac{-1-\sqrt{3} \mathrm{i}}{2}$, then the incorrect expression among the following is
A. $x^{3}+y^{5}=-1$
B. $x^{7}+y^{7}=-1$
C. $x^{9}+y^{9}=-1$
D. $x^{11}+y^{11}=-1$
2. C It is easy to know that $x=\omega, y=\omega^{2}$ (where $\omega$ is a cube root of unity), so $x^{9}+y^{9}=1+1=2$.