空白矩形框中应该填入的是（   ）

  Dim a As Integer, b As Integer

  a = Val(Text1.Text)

  If a Mod 2 = 0 Then

b = a + 1

ElseIf a Mod 3 = 0 Then

b = a + 2

ElseIf a Mod 5 = 0 Then

b = a + 4

  Else

b = a

  End If

  Label1.Caption = Str(b)

运行该程序，在文本框Text1中输入25，单击命令按钮Command1，在标签Label1中显示的是（   ）

Private Sub Command1_Click()

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

    n = Val(Text1.Text)

    s = ""

    For i = 1 To 2 * n - 1

        If i <= n Then  ① Else  ②  

Next i

    Label1.Caption = s

End Sub

为实现以上功能，划线①②处应分别填写（   ）

s=0

For i=1  to  5   step  -2

   s=s+i

Next i

执行上述代码后，下列说法正确的是（  ）

Const n = 8

Dim a(1 To n) As Integer

For i = 1 To n

    a(i) = Int(Rnd * 20)

Next i

x = n \ 2

For i = x To 2 Step -1

    For j = 1 To i - 1

      If a(j) < a(i) Then

        t = a(j): a(j) = a(i): a(i) = t

      End If

    Next j

Next i

i = n

Do While i > x + 1

    k = i

    For j = i - 1 To x + 1 Step -1

      If a(j) > a(k) Then k = j

    Next j

    If k <> i Then

      t = a(k): a(k) = a(i): a(i) = t

    End If

    i = i - 1

Loop

执行完这段代码后，数组 a 中各个元素的值可能的是（  ）

Dim i As Integer, s As String

i = 0

Do While i < 5

  s = Str(i) + s

  i = i + 1

Loop