I want to develop an enterprise app that includes a WindowsForms presentation layer, middle-tier components for business logic and data access, and a MsSQL Server database. Middle-tier components should contain some business objects and will be called from presentation layer using .NET Remoting. Whitch is the best way (and why) to reference these business objects from presentation layer?

a) Create class library project, implementing business objects. Reference this project from presentation layer and middle-tier layer.
b) Create interface library project defining business objects. Create class library project implementing interfaces. Reference class library project from middle-tier layer. Reference interface library project from presentation layer.
c) Create separate class library projects for middle-tier and presentation layer. Reference corresponding project from presentation layer.