class A
{
public int B { get; set; }
public string C { get; set; }
}
class Program
{
static void Main(string[] args)
{
List<A> list = new List<A>() {
new A(){ B=1,C="1"},
new A(){B=2,C="2"},
new A(){B=3,C="3"},
new A(){B=4,C="4"},
};
List<A> listT = new List<A>()
{
new A(){B=1,C="1"},
new A(){B=2,C="2"}
};

var aa = list.FindAll(c => !listT.Any(it => it.B == c.B)).ToList();
var bb = list.FindAll(c => listT.Any(it => it.B == c.B)).ToList();

//Files();
Console.Read();
}

}