one to many fluent api code

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MVC4

EF5.0

ASP.NET4

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Hi ,
Ihave one to many relatioin with section and category
category and subcateogry
and category to item , subcategory to item
in using EF code first and setting fluent api as

modelBuilder.Entity<Section>().HasMany(p => p.Categories).WithRequired().HasForeignKey(a => a.SectionID);
            modelBuilder.Entity<Category>().HasMany(p => p.Items).WithRequired().HasForeignKey(a => a.CategoryID);
            modelBuilder.Entity<Category>().HasMany(p => p.Subcategories).WithRequired().HasForeignKey(a => a.CategoryID);
            modelBuilder.Entity<Subcategory>().HasMany(p => p.Items).WithRequired().HasForeignKey(a => a.SubcategoryID);

please answers the questions
1. is this correct accoring to relationship
2. what will be code for one to one and one to 0..1 relationship