using System.Collections;
using System.Collections.Generic;
using System.Data.DataSetExtensions;
using System.Text.RegularExpressions;
using System.Globalization;
using System.Xml.Serialization;
public static void Main()
var lstA = new List<A>();
lstA.SelectMany(x=>x.listB.Select(y=>y.id)).Dump();
public List<B> listB {get;set;}