程序运行时，在Text1中输入字符串，单击“开始统计”按钮，在List1中显示统计结果。函数IsLetter(x)功能，若x是字母，则返回值为字母x在字母序列“A”~“Z”中的序号，如字母“A”的序号为0，字母“D”的序号为3。若x不是字母，则返回值为-1。

Function IsLetter(x As String) As Integer

        If "A" <= x And x <= "Z" Then

            IsLetter = Asc(x) - Asc("A")

        ElseIf "a" <= x And x <= "z" Then

            IsLetter = Asc(x) - Asc("a")

        Else

                       ①        

        End If

    End Function

    Private Sub Command1_Click()

        Dim d(25) As Integer, m As Integer, n As Integer

        Dim s As String, c As String

        List1.Clear

        For m = 0 To 25                  '初始化数组d

            d(m) = 0

        Next m

        s = Text1.Text

        For m = 1 To Len(s)              '读取字符串中的字符进行判断

            c = Mid(s, m, 1)

            n = IsLetter(c)

            If n <> -1 Then    ②  

        Next m

        For m = 0 To 25                  '输出结果

            If    ③   Then

               List1.AddItem (Chr(m + Asc("a")) & ":" & d(m))

            End If

        Next m

   End Sub

回答下列问题：

Dim tmp As Integer

Dim a(1 To 10) As Integer

Private Sub Command1_Click()

  For i=2 To 10

Text1.Text = ""

For i= 1 To 5

  For j=i+1 To 6

  If s(i) + s(i) < s(j) + s(i) Then

    t= s(j): s(j)= s(i): s(i)=t

  End If

  Next j

Next i

For i=1 To 6

  Text1.Text = s(i) + Text1.Text

Next i

  If  Then

    tmp = a(i)

      For j=  To 1 Step -1    ‘依次后移

        If tmp > a(j) Then Exit For

        a(j+1)= a(j)

      Next j

          ‘插入数据

    End If

  Next i

  For i= 1 To 10

    List1.Addltem a(i)

  Next i

End Sub

要实现上述功能，方框①②③中的语句分别是（  ）

For i= 1 To 3

For j= 1 To 5-i

     If a(j) >a(j+1) Then

         t=a(j)：a(j)=a(j+1)：a(j+1)=t

     End  If

     Next j

     Text 1．Text=Text 1．Text+str(a(i) )

Next i

数组元素a(1)到a(5)的值依次为“3，9，6，8，4”。该程序段执行后，文本框Text 1显示的内容是（  ）