When designing class hierarchies, why is "is-a" sometimes a misleading guide for inheritance (e.g. "a Square is-a Rectangle")?

A Because subclassing must always preserve behavioral expectations (LSP); a Square subclassing Rectangle can violate invariants if width/height are independently settable B Because squares and rectangles cannot both exist in the same program C Because inheritance is only allowed between numeric types D "Is-a" is never misleading and should always be followed literally