In logic, the intension (or connotation) of a term is the set of attributes or defining characteristics that the term implies, while its extension (denotation) is the collection of individual things to which it applies. These two are inversely related: as a term becomes more specific it packs in more attributes (greater intension) but applies to fewer things (smaller extension), and as it becomes more general it carries fewer attributes but covers more things.

Arranging the five terms in decreasing intension means starting with the most specific term (most attributes) and ending with the broadest term (fewest attributes):

• Wildcat — the most specific; it carries every attribute of being a wildcat and also all the attributes of being feline, mammalian, vertebrate and an animal, so it has the richest intension.
• Feline — the cat family; it drops the wildcat-specific traits but still adds cat-family attributes on top of mammal, vertebrate and animal.
• Mammal — warm-blooded, hair-bearing, nurses its young; broader than feline but narrower than vertebrate.
• Vertebrate — defined chiefly by possessing a backbone; broader than mammal.
• Animal — the broadest term with the fewest defining attributes, hence the smallest intension.

This produces the order Wildcat, Feline, Mammal, Vertebrate, Animal (B, C, A, E, D). The reversed sequences that begin with Animal are actually arrangements of increasing intension (equivalently, decreasing extension), which is the opposite of what the question asks; and any ordering that places Vertebrate before Mammal is wrong because every mammal is a vertebrate but not every vertebrate is a mammal, so mammal is the more specific of the two. The correct decreasing-intension order is B, C, A, E, D.