求助：不太理解程序内部的选题算法，不知道是不是随机的，c#

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class shijuanshengcheng_add : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
zhangjie.Items.Add("所有");
zhangjie.Items.Add("第一章");
zhangjie.Items.Add("第二章");
zhangjie.Items.Add("第三章");
}
}
protected void Button1_Click(object sender, EventArgs e)
{
string sql,nxuanzeti,nzhangjie,npanduanti,ntiankongti;
nxuanzeti = "";
npanduanti = "";
ntiankongti = "";
nzhangjie = zhangjie.Text.ToString().Trim();
int nxuanzetishu = int.Parse(xuanzetishu.Text.ToString().Trim());
int npanduantishu = int.Parse(panduantishu.Text.ToString().Trim());
int ntiankongtishu = int.Parse(tiankongtishu.Text.ToString().Trim());
int i = 0;
sql = "select top " + nxuanzetishu + " id from xuanzeti where 1=1";
if (nzhangjie != "所有")
{
sql = sql + " and zhangjie='"+nzhangjie+"'";
}
sql=sql+" order by newid()";
DataSet result2 = new DataSet();
result2 = new Class1().hsggetdata(sql);
if (result2 != null)
{
for (i = 0; i < nxuanzetishu; i++)
{
nxuanzeti = nxuanzeti + result2.Tables[0].Rows[i][0].ToString().Trim() + ",";
}
nxuanzeti = nxuanzeti.Substring(0, nxuanzeti.Length - 1);
}
sql = "select top " + npanduantishu + " id from panduanti where 1=1";
if (nzhangjie != "所有")
{
sql = sql + " and zhangjie='" + nzhangjie + "'";
}
sql = sql + " order by newid()";
result2 = new Class1().hsggetdata(sql);
if (result2 != null)
{
for (i = 0; i < npanduantishu; i++)
{
npanduanti = npanduanti + result2.Tables[0].Rows[i][0].ToString().Trim() + ",";
}
npanduanti = npanduanti.Substring(0, npanduanti.Length - 1);
}
sql = "select top " + ntiankongtishu + " id from tiankongti where 1=1";
if (nzhangjie != "所有")
{
sql = sql + " and zhangjie='" + nzhangjie + "'";
}
sql = sql + " order by newid()";
result2 = new Class1().hsggetdata(sql);
if (result2 != null)
{
for (i = 0; i < ntiankongtishu; i++)
{
ntiankongti = ntiankongti + result2.Tables[0].Rows[i][0].ToString().Trim() + ",";
}
ntiankongti = ntiankongti.Substring(0, ntiankongti.Length - 1);
}
sql = "insert into shijuanshengcheng(shijuanbianhao,zhangjie,xuanzetishu,xuanzetifenzhi,panduantishu,panduantifenzhi,tiankongtishu,tiankongtifenzhi,xuanzeti,panduanti,tiankongti) values('" + shijuanbianhao.Text.ToString().Trim() + "','" + zhangjie.Text.ToString().Trim() + "','" + xuanzetishu.Text.ToString().Trim() + "','" + xuanzetifenzhi.Text.ToString().Trim() + "','" + panduantishu.Text.ToString().Trim() + "','" + panduantifenzhi.Text.ToString().Trim() + "','" + tiankongtishu.Text.ToString().Trim() + "','" + tiankongtifenzhi.Text.ToString().Trim() + "','" + nxuanzeti + "','"+npanduanti+"','"+ntiankongti+"') ";
int result;
result = new Class1().hsgexucute(sql);
if (result == 1)
{
Response.Write("<script>javascript:alert('添加成功');</script>");
}
else
{
Response.Write("<script>javascript:alert('系统错误，请检查数据库设置问题');</script>");
}
}
}