When I'm using C# to write some code and I define an interface using Visual Studio 2010, it always includes a number of "using" statements (as shown in the example)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace TestEngine.TestNameSpace
{
    interface ITest1
    {
        bool testMethod(int xyz);
    }
} 

I wonder what these are for and if they are really necessary. Can I leave these out? Are they only necessary when I'm using those parts in my interface description?