Which of the following is a low-level cloud that is smooth in appearance?

Stratus clouds are classified as low-level clouds and are characterized by their smooth, uniform appearance, often resembling a gray blanket covering the sky. These clouds typically form in stable atmospheric conditions and can result in overcast skies, mist, or light drizzle. Their smooth and featureless appearance distinguishes them from other types of clouds that may exhibit more texture and vertical development, such as cumulus or cumulonimbus clouds.

In comparison, cumulonimbus clouds are towering, vertical structures associated with thunderstorms, while altostratus and altocumulus clouds are higher clouds that can have more texture and may display varying degrees of thickness and sunlight penetration. The characteristics of stratus clouds, therefore, make them the clear choice for identifying a low-level cloud with a smooth appearance.