static void Main()
{
A
a = new A();
Console.WriteLine(a.IsEven(4));
//Console.WriteLine(a.IsOdd(3)); // Cannot access explicit implementation of 'IEven.IsOdd'
Console.WriteLine(((IEven)a).IsOdd(3));
var derived = new Derived();
derived.A();
derived.B();
var iderived = derived as II;
iderived.B();
}