程序运行时，选择一个文本文件，读取该文件中的内容，对数字字符进行加密，加密方法如下：0-＞3,1-＞4……7-＞0,8-＞1,9-＞2。结果在文本框显示。 Private Sub Button1_Click（) Handles Button1.Click Dim i, n, t As Integer Dim s1, str, c As String If OpenFileDialog1.ShowDialog = Windows.Forms.DialogResult.OK Then FileOpen（1, OpenFileDialog1.FileName, _____（1)_____) Do While _____（2)_____ s1 = _____（3)_____ str &= s1 & vbCrLf Loop FileClose（) n = Len（str) For i = 1 To n c = Mid（str, i, 1) If ___