What is the difference between "structural subtyping" and "nominal subtyping"?

A Structural subtyping determines compatibility based on the shape (members) of a type, while nominal subtyping requires an explicit declared relationship (e.g. extends/implements) B They are two names for the exact same mechanism in every language C Structural subtyping only applies to numbers, nominal subtyping only to strings D Nominal subtyping is determined entirely at runtime with no declarations