Interfaces - General Questions

Which interface lets a collection be initialised with { } syntax and supports Add and Count?

What is the main difference between an abstract class and an interface?

What is explicit interface implementation?

What is the output of the following program?

var d = new Duck();
Console.WriteLine(((IFly)d).Move() + ((ISwim)d).Move());
interface IFly { string Move(); }
interface ISwim { string Move(); }
class Duck : IFly, ISwim
{
    string IFly.Move() => "fly";
    string ISwim.Move() => "swim";
}

Which interface enables the using statement for releasing resources?