我想做个在线测试，需要随机出题，所以要动态的添加n多控件 ，但是在.net2.0里面动态添加的控件，postback 后都消失了，不知道怎么办啊。代码如下

    protected void btnRandom_Click(object sender, EventArgs e)
    {
        DataSet ds = testBLL.Test(Convert.ToInt32(this.tbNumber.Text), "");

        this.pSelect.Visible = false;
        pTest.Visible = true;

        for (int loop = 0; loop < ds.Tables[0].Rows.Count; loop++ )
        {
            buildTest(ds.Tables[0].Rows[loop],loop);
        }

        this.pTest.Controls.Add(btnFinish);
    }

 protected void buildTest(DataRow dr, int loop)
    {
        David.Nephropathy.Model.test testData = new David.Nephropathy.Model.test();
        testData.id = Convert.ToInt32(dr["id"]);
        testData.title = dr["title"].ToString();
        testData.type = dr["type"].ToString();
        testData.answer = dr["answer"].ToString();
        testData.A = dr["A"].ToString();
        testData.B = dr["B"].ToString();
        testData.C = dr["C"].ToString();
        testData.D = dr["D"].ToString();
        testData.E = dr["E"].ToString();
        testData.F = dr["F"].ToString();

        Label lbl = new Label();
        lbl.ID = "t_" + testData.type + "_" + testData.id.ToString();
        Literal ltTitle = new Literal();
        ltTitle.Text = (loop + 1).ToString() + " . " + testData.title + "<br>";
        lbl.Controls.Add(ltTitle);
        switch (testData.type)
        { 
            case "单选题":
                RadioButtonList rbl = new RadioButtonList();
                if (testData.A != string.Empty)
                    rbl.Items.Add(new ListItem("A:" + testData.A, "A"));
                if (testData.B != string.Empty)
                    rbl.Items.Add(new ListItem("B:" + testData.B, "B"));
                if (testData.C != string.Empty)
                    rbl.Items.Add(new ListItem("C:" + testData.C, "C"));
                if (testData.D != string.Empty)
                    rbl.Items.Add(new ListItem("D:" + testData.D, "D"));
                if (testData.E != string.Empty)
                    rbl.Items.Add(new ListItem("E:" + testData.E, "E"));
                if (testData.F != string.Empty)
                    rbl.Items.Add(new ListItem("F:" + testData.F, "F"));
                lbl.Controls.Add(rbl);

                break;
            case "多选题":
                CheckBoxList cbl = new CheckBoxList();
                if (testData.A != string.Empty)
                    cbl.Items.Add(new ListItem("A:" + testData.A, "A"));
                if (testData.B != string.Empty)
                    cbl.Items.Add(new ListItem("B:" + testData.B, "B"));
                if (testData.C != string.Empty)
                    cbl.Items.Add(new ListItem("C:" + testData.C, "C"));
                if (testData.D != string.Empty)
                    cbl.Items.Add(new ListItem("D:" + testData.D, "D"));
                if (testData.E != string.Empty)
                    cbl.Items.Add(new ListItem("E:" + testData.E, "E"));
                if (testData.F != string.Empty)
                    cbl.Items.Add(new ListItem("F:" + testData.F, "F"));
                lbl.Controls.Add(cbl);
                break;
            case "简答题":        
            case "问答题":
                TextBox tb = new TextBox();
                tb.Height = Unit.Pixel(50);
                tb.Width = Unit.Pixel(500);
                lbl.Controls.Add(tb);
                break;
        }

        Literal ltAnswer = new Literal();
        ltAnswer.ID = "answer" + testData.id.ToString();
        ltAnswer.Text = testData.answer;
        ltAnswer.Visible = false;
        lbl.Controls.Add(ltAnswer);

        

        this.pTest.Controls.Add(lbl);

    }