构造控件出错求解啊.(0分)

请问为何我下面构造ADO连接控件的程序,在运行的时候,总是弹出下面的出错来?
Field form1.ad does not have a corresponding component remove the declaration?

type
TForm1 = class(TForm)
ad:tadoquery;
data:tdatasource;
procedure FormCreate(Sender: TObject);

private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
ad:=tadoquery.create(self);
data:=tdatasource.create(self);
end;

把变量申明移到private或者public中。