14 Acute angles $\alpha, \beta$ satisfy the condition $\frac{\sin ^{4} \alpha}{\cos ^{2} \beta}+\frac{\cos ^{4} \alpha}{\sin ^{2} \beta}=1$, which of the following conclusions is correct?
A. $\alpha+\beta>\frac{\pi}{2}$
B. $\alpha+\beta<\frac{\pi}{2}$
C. $\alpha+\beta \neq \frac{\pi}{2}$
D. $\alpha+\beta=\frac{\pi}{2}$