图1
   图2

 程序代码如下：

Private Sub Command1_Click()

  Dim i As Integer

  List1.Clear            '清除列表框内容

End Sub

Private Function f(x As Integer) As Boolean  '自定义函数f,返回值为逻辑型

  Dim j As Integer

  f = True

  For j = 2 To Int(Sqr(x))

    If x Mod j = 0 Then

      f =     ③      '函数返回值

      Exit For           '跳出For循环

    End If

  Next j

End Function

Private Sub Command1_Click()

 Dim i As Integer, m As Integer, n As Integer

    Label1.Caption = "1000以内的完全数如下："

    For i = 1 To 1000

        n = 0

        For m = 1 To i \ 2

            If i Mod m = 0 Then n = n + m

        Next

        If n = i Then Label2.Caption = Label2.Caption & "" & Str(i)

    Next

End Sub

该过程采用的算法是（    ）

实现上述功能的VB代码如下：

Private Sub Command1_Click() Dim a(0 To 4) As String Dim b(0 To 4) As Integer

Dim s As String, r As String

Dim i As Integer, j As Integer, k As Integer, c As Integer, n As Integer

List1.Clear

s = Text1.Text :   n = Len(s)

If         Then    '选填 Label1.Caption = "数据输入有误！"

Exit Sub   '退出 End If

For i = 0 To n - 1

a(i) = Mid(s, i + 1, 1) b(i) = 0

Next i c = 0

For i = 1 To n ^ n r = ""

For j = 0 To n - 1

Next j

c = c + 1 List1.AddItem r k = 0

b(k) = b(k) + 1

Do While b(k) = n And k < 4 b(k) = 0

b(k) = b(k) + 1 Loop

Next i

Label1.Caption = "构造字符串的方法共计" + Str(c) + "种。" End Sub

Function test(s As String) As Boolean ‘用于判别是否存在重复的字符，代码略

‘若无重复，则返回True，否则返回False

End Function

请回答下列问题：

Private Sub Command1_Click()

 i＝1

 j＝7

 Do While ____①____

i＝____②____

j＝____③____

 Loop

 Text1.Text＝Str(i)

 Text2.Text＝Str(j)

End Sub

则下列说法正确的是（  ）