What is the proper way to implement an interface that has its own interface members? (am I saying that correctly?) Here's what I mean:

public Interface IFoo
{
    string Forty { get; set; }
    string Two { get; set; }
}

public Interface IBar
{
    // other stuff...

    IFoo Answer { get; set; }
}

public class Foo : IFoo
{
    public string Forty { get; set; }
    public string Two { get; set; }
}

public class Bar : IBar
{
    // other stuff

    public Foo Answer { get; set; } //why doesnt' this work?
}

I've gotten around my problem using explicit interface implementation, but I'm wondering if there is a better way?