How do I define a generic class that implements an interface and constrains the type parameter?

class Sample<T> : IDisposable // case A
{
    public void Dispose()
    {
        throw new NotImplementedException();
    }
}

class SampleB<T> where T : IDisposable // case B
{
}

class SampleC<T> : IDisposable, T : IDisposable // case C
{
    public void Dispose()
    {
        throw new NotImplementedException();
    }
}

Case C is the combination of case A and case B. Is that possible? How to make case C right?