Please choose the correct ending to complete the given sentence: Education and Communications: [header] How to distinguish the different types of clouds [title] Identify clouds by shape. [step] The two shapes are cumulus and stratus : [substeps] Cumulus clouds: these are the big, " fluffy " clouds that look a bit like cotton balls. These clouds have a thickness that is usually equal to or greater than their width and they have very distinct edges.

Ending1: Stratus clouds: these clouds are very light gray with wider edges than the biggest ones. Stratus clouds are darker, with a thicker " grain " that has an opaque appearance than the largest ones. Ending2: Stratus clouds are the long, dense, " flat " clouds. Stratus clouds also have a rough shape, like a ball of grass or coral that is round and has a slightly raised surface. Ending3: Cumulus clouds tend to indicate that the atmosphere is unstable at the altitude where they are found. Stratus clouds: these clouds are layered and often look flat. Ending4: Stratus: these are the large, " plumped " clouds, and are most recognizable when seen from the sky. Stratus clouds are distinguishable by their color.

Answer format: ending1/ending2/ending3/ending4