5. For any $\varphi \in\left(0, \frac{\pi}{2}\right)$, we have
(A) $\sin \sin \varphi\cos \varphi>\cos \cos \varphi$;
(C) $\sin \cos \varphi>\cos \varphi>\cos \sin \varphi$;
(D) $\sin \cos \varphi<\cos \varphi<\cos \sin \varphi$.
5. (D)

Since in $\left(0, \frac{\pi}{2}\right)$, $\sin x\sin \varphi, \cos x$ are monotonically decreasing, we have
$$
\cos \varphi < \cos (\sin \varphi).
$$
$\therefore \quad \sin \cos \varphi < \cos \varphi < \cos \sin \varphi$ holds.