c# - !IsPostBack の何が問題なのですか?

Question

protected void Page_Load(object sender, EventArgs e)
{   
if(!IsPostBack)
{
LoadQuestion(); //randomly choose question from database and put inside panel1
LoadQuestion1();//randomly choose question from database and put inside panel2
Panel1.visible=true;
Panel2.visible=false;
}

void LoadQuestion()
{
while (dtr.Read())
{
question[index, 0] = dtr["Question"].ToString().Trim();
question[index, 1] = dtr["OptionA"].ToString().Trim();
question[index, 2] = dtr["OptionB"].ToString().Trim();
question[index, 3] = dtr["OptionC"].ToString().Trim();
question[index, 4] = dtr["OptionD"].ToString().Trim();
question[index, 5] = dtr["Answer"].ToString().Trim();
question[index, 6] = dtr["QuestionNo"].ToString().Trim();
index++;
}
for(i=0;i<10;i++)
{
 Label lbl = new Label();
 RadioButtonList rad = new RadioButtonList();
 lbl.ID = "lbl" + i.ToString();
 rad.ID = "rad" + i.ToString();

 lbl.Text = i + ". " + question[num, 0].ToString();
 rad.Items.Add(question[i, 1]);
 rad.Items.Add(question[i, 2]);
 rad.Items.Add(question[i, 3]);
 rad.Items.Add(question[i, 4]);
 Panel1.Controls.Add(lbl);
 Panel1.Controls.Add(rad);
}
}



void LoadQuestion1()
{

for(i=11;i<20;i++)
{
 Label lbl = new Label();
 RadioButtonList rad = new RadioButtonList();
 lbl.ID = "lbl" + i.ToString();
 rad.ID = "rad" + i.ToString();

 lbl.Text = i + ". " + question[num, 0].ToString();
 rad.Items.Add(question[i, 1]);
 rad.Items.Add(question[i, 2]);
 rad.Items.Add(question[i, 3]);
 rad.Items.Add(question[i, 4]);
 Panel2.Controls.Add(lbl);
 Panel2.Controls.Add(rad);
}
}

protected void lb1_Click(object sender, EventArgs e)
{
Panel1.Visible = true;
Panel2.Visible = false;
}

protected void lb2_Click(object sender, EventArgs e)
{
Panel2.Visible = true;
Panel1.Visible = false;
}

この場合、!IsPostBackPage_Load 内に配置しなかった場合、 または をクリックすると、質問が変化lb1し続けlb2ます。 . どうしたの？!IsPostBackPage_Loadlb1lb2Panel1Panel2