编写VB程序，实现如下功能：单击“生成密文”按钮Command2，在文本框Text3中产生与每个小写字母对应的密文（每个明文字母对应1个不重复的密文字母）。在文本框Text1中输入单词字符串，单击“加密”按钮Command1后，进行逐个字符加密，加密方法：在“明文”中找到相应字符，再得到明文对应位置的密文,并在文本框Text2中显示对应密文（运行效果如图所示）。实现上述功能的VB代码如下：

Dim m2 As String
Private Sub Command1_Click()
Dim flag(1 To 26) As Boolean
Dim num As Integer,t As Integer
Randomize
num = 1
Text3.Text = " "
For i =" 1" To 26
flag(i) = False
Next i
Do While num <= 26
x =" Int(Rnd" * 26) + 97
  ①
If  flag(t) =" False" Then
m2 =" m2" + Chr(x)
num =" num" + 1
② 
End If
Loop
Text3.Text = m2
End Sub
Private Sub Command2_Click()
Dim s As String， m As String， result As String
Dim k As String， c As Integer
s = Text1.Text
m = "abcdefghijklmnopqrstuvwxyz"
For i =" 1" To Len(s)
k =" Mid(s," i, 1)
If  k >= "A" And k <= "Z"  Then
k =" Chr(Asc(k)" + 32)
End If
c =" 1:" continue = True
Do While③  
If k =" Mid(m," c, 1) Then
continue = False
End If
c =" c" + 1
Loop
④ 
Next i
Text2.Text = result
End Sub
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程序③处的代码是
程序④处的代码是