What is a defining feature of stratus clouds?

Stratus clouds are characterized by their low altitude and sheet-like appearance, often covering the sky like a blanket. This uniformity can lead to overcast conditions, where the clouds appear as a continuous layer that obscures the sun. The low position of these clouds usually results in light rain or drizzle, which further distinguishes them from other types of clouds that may be more isolated or have greater vertical development.

The other options do not accurately describe stratus clouds. High altitudes typically pertain to types of clouds like cirrus or altostratus, which are found much higher in the atmosphere. The mention of reflective characteristics is more relevant to clouds in general, but does not specifically highlight what defines stratus clouds. Additionally, the association of stratus clouds with severe thunderstorms is incorrect, as such conditions are generally linked to cumulonimbus clouds instead, which have a very different structure and formation process. Thus, the defining feature of stratus clouds is best represented by their low-lying and sheet-like appearance.