Question

which description refers to stratus clouds?
are thin and wispy
are round and fluffy
cover all or most of the sky
form at high altitudes

Explanation:

Stratus clouds are low - level clouds that often cover the entire sky or most of it. They are usually gray and can bring light rain or drizzle. Thin and wispy clouds are cirrus clouds. Round and fluffy clouds are cumulus clouds. Clouds that form at high altitudes are cirrus, cirrostratus, or cirrocumulus clouds.

Answer:

cover all or most of the sky