在text1文本框内输入字符串，单击去重按钮，将字符串后面相同的字符删除，并在text2中输出经过删除的字符串。程序界面如图所示。请在下面划线处填入合适的代码。 
Private Sub Command1_Click()
Dim s As String, s1 As String, c As String
s = Text1.Text
For i = 1 To Len(s)
c = Mid(s, i, 1)
s1 = ⑴
For j = ⑵
If c <> Mid(s, j, 1) Then
s1 = s1 + Mid(s, j, 1)
End If
Next j
⑶
Next i
Text2.Text = s
End Sub
