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-altitude, layered clouds that spread out widely, creating a uniform, overcast sky. Thin/wispy describes cirrus clouds, round/fluffy describes cumulus clouds, and high-altitude formation is characteristic of cirrus clouds.

Answer:

cover all or most of the sky