随机问题，（急）(100分)

我想从20个学生中随机抽取5个学生，该怎么实现啊，先谢了

Randomize;
//初始化
RandomRange(1, 20);
//随即产出1到20的数

procedure TForm1.Button4Click(Sender: TObject);
var L1,L2:TList;
I,K:Integer;
begin
L1:=TList.Create;
L2:=TList.Create;
for I:=1 to 20do
L1.Add(Pointer(I));
Randomize;
for I:=1 to 5do
begin
K:=Random(L1.Count-1);
L2.Add(L1[K]);
L1.Delete(K);
end;
for I:=0 to 4do
ShowMessage(IntToStr(Integer(L2)));
L1.Free;
L2.Free;
end;

能不能使用如下方式:
st:=query1.recordcount;
sel:=10;
f:=1;
while(f<sel)do
begin
num:=random(st)+1;
query1.first;
query1.moveby(num-1);
...
f:=f+1;
end;

但这样做会产生相同的记录，特别是sel和st接近时，怎样才能不会有相同的记录呢？
请解决!

procedure TForm1.Button4Click(Sender: TObject);
var L1:TList;
I,num,sel:Integer;
begin
L1:=TList.Create;
try
for I:=0 to query1.recordcount-1do
L1.Add(Pointer(I));
sel:=10;
Randomize;
for I:=1 to seldo
begin
num:=Random(L1.Count-1);
query1.first;
query1.moveby(num);
L1.Delete(num);
...........
end;
finally
L1.Free;
end;
end;

谢谢