A：${\sin }^2\alpha +{\cos }^2\beta +\sin \alpha \cos \beta =\frac{3}{4}$

B：${\sin }^2\left(\alpha -30°\right)+{\cos }^2\alpha +\sin \left(\alpha -30°\right)\cos \alpha =\frac{3}{4}$

C：${\sin }^2\left(\alpha -15°\right)+{\cos }^2\left(\alpha +15°\right)+\sin \left(\alpha -15°\right)\cos \left(\alpha +15°\right)=\frac{3}{4}$

D：${\sin }^2\alpha +{\cos }^2\left(\alpha +30°\right)+\sin \alpha \cos \left(\alpha +30°\right)=\frac{3}{4}$