某 VB 段程序如下：
s = Text1.Text
For i = 1 To Len(s) c = Mid(s, i, 1)
s1 = s1 + c Next i Text2.Text = s1
程序运行时，在文本框Text1中输入“ABC123xyz”，在文本框Text2中输出“bcd123yza”，则加框①处的代码为（ ）
A.
A、If c >= "A" And c <= "Z" Then c = Chr(Asc(c)+ 32) If c >= "a" And c <= "z" Then m = (Asc(c) - Asc("a") + 1) Mod 26 c = Chr(m + Asc("a")) End If
B、If c >= "A" And c <= "Z" Then c = Chr(Asc(c) + 32) ElseIf c >= "a" And c <= "z" Then m = (Asc(c) - Asc("a") + 1) Mod 26 c = Chr(m + Asc("a")) End If
C、If c >= "A" And c <= "Z" Then c = Chr(Asc(c)+32) If c >= "a" And c <= "z" Then m = (Asc(c) - Asc("a") ) Mod 26+1 c = Chr(m + Asc("a")) End If
D、If c >= "A" And c <= "Z" Then c = Chr(Asc(c) + 32) ElseIf c >= "a" And c <= "z" Then m = (Asc(c) - Asc("a")) Mod 26 + 1 c = Chr(m + Asc("a")) End If
