怎么判断子类是不是某类的子类

如何判断子类是不是某类的子类？
比如有个父类A，有若干子类B,C等，如何判断类B，类C是从类A继承的？

[解决办法]
你看下面的代码就知道了，判断一个类的父类。
unit Unit1;

interface

uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;

type
TForm1 = class(TForm)
Button1: TButton;
Label1: TLabel;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
begin
showmessage(Label1.ClassName);
showmessage(Label1.ClassParent.ClassName);
showmessage(Label1.ClassParent.ClassParent.ClassName);
end;

end.
[解决办法]
InheritsFrom()

如:
 if Button1.InheritsFrom(TButton) then
showmessage('TButton是Button1的祖先');

 if B.InheritsFrom(A) then
showmessage('A是B的祖先');