图a

图b为标准ASCII码表供你参考（其中ASCII为1-32,127的字符为特殊符号，不能用作密码）：

图b

实现上述功能的VB程序代码如下，请回答以下问题：

Private Sub Command1_Click()

  Dim a(0 To 5) As Integer

  Dim i As Integer               ’①

  a(0) = 1                      '②

  For i = 1 To 5

    a(i) = 2 * a(i - 1) + 1          '③

  Next i

  Text1.Text = Str(a(6))         '④

End Sub

      flag = True : i = 1

      Do While i <= 6

          x = Int(Rnd * 100) + 1 

          If flag Or x >50 Then

               a(i)=x

               flag = Not flag

               i = i + 1

          End if

      Loop

执行该程序段后，在下列选项中，a（1）～a（6）各元素值不可能的是（  ）

 Dim a(1 To 10) As Integer

 Dim s(1 To 10) As Integer

 Private Sub Form_Load()

  a(1) = 3: a(2) = 6: a(3) = 8: a(4) = 4: a(5) = 9

  a(6) = 5: a(7) = 3: a(8) = 3: a(9) = 10: a(10) = 5

 End Sub

 Private Sub Command1_Click()

 Dim i As Integer, t As Integer

 s(1) = a(1)

 For i = 2 To 10

  s(i) = s(i - 1) + a(i)

 Next i

 t = s(8) - s(4)

 Text1.Text = Str(t)

End Sub

程序运行后，文本框Text1显示的内容是（  ）

lst = [2,5,2,1]

y = [1,1,1,1]

n = len(lst)

for i in range(①____):

    for j in range(②____):

        if ③____:

            y[j] = y[j] + 1

        else

            y[i] = y[i] + 1

上述程序段3个划线处的表达式分别为（   ）