怎么调用类文件

我在我的站点中定义了一个db.cs类文件怎么在页面中调用呢？
例如：

public class DB:System.Web.UI.Page
{
    public DB()
    {
        //
        // TODO: 在此处添加构造函数逻辑
        //
    }
    public static OleDbConnection DBconntion()
    {
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source="+HttpContext.Current.Server.MapPath("app_data/it.mdb");
        return conn;
    }
    public static DataTable DBtable(string sql)
    {
        OleDbConnection conn = new OleDbConnection();
        conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + HttpContext.Current.Server.MapPath("app_data/it.mdb");
        conn.Open();
        OleDbCommand comm = new OleDbCommand(sql,conn);
        OleDbDataAdapter da = new OleDbDataAdapter();
        da.SelectCommand = comm;
        DataSet ds = new DataSet();
        da.Fill(ds);
        conn.Close();
        return ds.Tables[0] ;
    }}


怎么在后边调用它呢？

 
    OleDbConnection conn;
    OleDbCommand DBtable;
    protected void Page_Load(object sender, EventArgs e)
    {
        conn = DB.DBconntion();
        conn.Open();
        //OleDbConnection conn = new OleDbConnection();
        //conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" + Server.MapPath("app_data/it.mdb");
        //conn.Open();


        string sql = "select * from zx";
        DB dt = new DB();
        DataTable dts = DB.DBtable();
                
      
        //OleDbCommand comm = new OleDbCommand(sql, conn);
        //OleDbDataAdapter da = new OleDbDataAdapter();
        //da.SelectCommand = comm;
        //DataSet ds = new DataSet();
        //da.Fill(ds);
        //conn.Close();


        DataList1.DataSource =dts;
        DataList1.DataBind();
    }
这样写的话红色的部分报错！！
要怎么写呢？