某程序段如下：

s = "happy": n = Len(s)

For i = 1 To n

  x = Int(Rnd * n + 1)

  c = Mid(s, x, 1)

  If x Mod 2 = 0 Then

    c = Chr((Asc(c) - Asc("a") + 1) Mod 26 + Asc("a"))

  Else

    c = Chr(Asc("a") + 25 - (Asc(c) - Asc("a")))

  End If

  s1 = c + s1

Next i

则运行本程序段后，变量s1的值不可能为（   ）

A、"bbkkq"

B、"qbqsq"

C、"kksqk"

D、"gboqx"