怎样去掉列中重复的项？
实践作业：要求用VB2010+ACCESS2007做一个选择省出现对应城市的二级联动

现已完成的代码如下：
Public Class Form1

Dim connectionstring As String ''定义连接字符串


Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

''对连接数据库的字符串赋值
connectionstring = "Provider = Microsoft.ACE.OLEDB.12.0;Data Source=" & My.Application.Info.DirectoryPath & "\MyDB.accdb;" '路径为E:\VBtext\text\text\bin\MyDB.accdb
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
''控件连接数据库并显示数据
Dim querystring As String = "select * from cs"
Dim conn As New OleDb.OleDbConnection(connectionstring)
Try
conn.Open()
Dim cmd As New OleDb.OleDbCommand(querystring, conn)
Dim reader As OleDb.OleDbDataReader
reader = cmd.ExecuteReader() '执行读取命令

ComboBox1.Items.Clear() '清空现有内容
While (reader.Read())
ComboBox1.Items.Add(reader.GetValue(1)) '添加省份
End While

reader.Close()
Catch ex As Exception
MsgBox(ex.Message)
End Try

End Sub

End Class


运行后的结果如图：



现在想要做的是：把省这个下拉框中的重复项去掉

我知道在SQL语句中省前加DISTINCT即可，可我的程序该怎么弄呀？

各位大虾帮帮忙哦~！~~~~~不胜感激！~~~~~~~~~先谢过啦！~~~~~~~

[解决办法]
Add之前，先用IndexOf检查是否存在
[解决办法]
While (reader.Read())
if(ComboBox1.Items.Contains(reader.GetValue(1)))
continue
ComboBox1.Items.Add(reader.GetValue(1)) '添加省份
End While