Which cloud type appears as a white sheet with a pebbly pattern?

The correct answer is Cirrocumulus. This cloud type is characterized by its thin, white appearance and distinct pattern that resembles a pebbly or rippled texture. Cirrocumulus clouds typically form at high altitudes, and their structure consists of small, rounded white patches or layers that can cover large areas of the sky.

These clouds are made up of ice crystals due to the high altitudes at which they form, hence they often indicate fair weather, but can also signal a change in the weather. Their unique aesthetic, often described as a "mackerel sky," adds to their identification.

In contrast, the other cloud types do not match this description. Stratus clouds appear as uniform gray sheets that cover the sky, lacking any texture. Nimbostratus clouds are thick, dark, and associated with persistent precipitation, showing more of a solid layer rather than a pebbly pattern. Finally, cumulus fractus clouds are fragmented, low-level clouds that can look like broken bits of cumulus, but do not exhibit the characteristic high-altitude texture or the "sheet" appearance that cirrocumulus clouds do.