5. The curve represented by the equation $\frac{x^{2}}{\sin \sqrt{2}-\sin \sqrt{3}}+\frac{y^{2}}{\cos \sqrt{2}-\cos \sqrt{3}}=1$ is
A. An ellipse with foci on the $x$-axis
B. A hyperbola with foci on the $x$-axis
C. An ellipse with foci on the $y$-axis
D. A hyperbola with foci on the $y$-axis
Since the graph of the function $y=\sin x$ is symmetric about the line $x=\frac{\pi}{2}=1.57$, $\sqrt{2}=1.414 \in\left(0, \frac{\pi}{2}\right)$, $\sqrt{3}=1.732 \in\left(\frac{\pi}{2}, \pi\right)$, and $1.57-1.414=0.1560, \cos \sqrt{2}-\cos \sqrt{3}>0$. Also, $\sin \sqrt{2}-\sin \sqrt{3}<\cos \sqrt{2}-\cos \sqrt{3} \Leftrightarrow \sin \sqrt{2}-\cos \sqrt{2}<\sin \sqrt{3}-\cos \sqrt{3}$, which is obviously true. Therefore, the original equation represents an ellipse with its foci on the $y$-axis, i.e., the answer is $C$.