If you dug down into the accumulation zone of a glacier, you would find three main layers. The top layer is snow that thickens further up the glacier. Below this layer is firn, a transitional layer between snow and ice, which is as hard as ice but not as dense. The deepest layer is ice.
The answer is C=territoriality This is so because Al's cat may have seen another cat in his 'home'. Cats don't like it when other cats trespass into their territory, so this is a way of marking it.
