1. (2019·上海模拟) 有如下VB 程序：

Private Sub Command1_Click()

    Dim i As Integer, j As Integer, k As String, n As Integer, s As String

    s = "abcdefghijklmn"

    n = 4

    List1.Clear

    For i = 1 To n

        k = Mid(s, i + 1, i)

        For j = 1 To Len(k)

            k = k + Mid(s, j, 1)

        Next j

        List1.AddItem k

    Next i

End Sub

该程序运行后，在列表框List1中显示的是（   ）

A . B . C . D .