4. For angles $\alpha$ and $\beta$, if $\sin \alpha \sin \beta+\cos \alpha \cos \beta=0$ then the value of $\sin 2 \alpha+\sin 2 \beta$ is
A. 0
B. 1
C. $\sqrt{2}$
D. Greater than $\sqrt{2}$
4. From $\sin \alpha \sin \beta+\cos \alpha \cos \beta=0$ we get $\cos (\alpha-\beta)=0, \sin 2 \alpha+\sin 2 \beta=2 \sin (\alpha+\beta) \cos (\alpha-\beta)=0$