Which cloud generally appears as thin white streaks?

Correct answer: Cirrus clouds

Correct answer: C, cirrus clouds. Cirrus clouds are high-altitude clouds that usually appear as thin, delicate, white streaks or feathery threads across the sky. At their great height, temperatures are very low, so they are composed mainly of ice crystals. Their thin appearance is also related to the small amount of cloud material spread through the upper atmosphere. Option A is wrong because cumulus clouds are generally puffy, rounded, and vertically developed. Option B is wrong because nimbus is a term associated with rain-bearing clouds, not the specific thin, streaky appearance described here. Option C is correct because cirrus has a wispy, fibrous form. Option D is wrong because dense fog is a cloud-like collection of droplets near the ground and usually reduces visibility rather than forming high white streaks. Memory cue: cirrus looks like fine brush strokes or feathers high in the sky.