设计VB程序，实现功能：将每个科目的选课人数按照选考人数降序排序后输出。其中，科目名称存放在数组a(i)中，人数存放在数组b(i)中。

程序运行界面设计如图所示，左边列表框List1是显示科目名称和选课人数，单击“排序”按钮Command1后，在右边的列表框List2中显示排序后的科目名称和选课人数。

Command1的处理事件过程如下，但加框处代码有错，请改正。

Private Sub command1_click()

Dim a(1 To 7)  As String

Dim b(1 To 7)  As Integer

Dim i As Integer, j As Integer, p As String, q As Integer

For i = 1 To 7

   List1.AddItem a(i) + " " + Str(b(i))

Next i

For i = 1 To 6

   k = i

   For j = i + 1 To 7

Next j

   If i <> k Then

     p = a(i): a(i) = a(k): a(k) = p

   End If

Next i

For i = 1 To 7

   List2.AddItem a(i) + " " + Str(b(i))

Next i

End Sub
①{#blank#}1{#/blank#}   ②{#blank#}2{#/blank#}

    Const n=5

    For i=1 To 2

      For j=n-1 To i step-1

         If a(j)>a(j+1) Then

           t=a(j)：a(j)=a(j+1)：a(j+1)=t

         End If

      Next j

  Next i

数组元素a(1)到a(5)的值依次为“33，24，45，16，77”，经过该程序段“加工”后，数组元素a(1)到a(5)的值依次为（  ）

Const n = 10

Dim a(1 To n) As Integer

Private Sub Command1_Click()

Dim i As Integer, j As Integer, t As Integer

Dim bottom As Integer

'获取排序前数据依次存储在数组a中，并在文本框Text1中显示。代码略

bottom = n

i = 1

Do While i <= bottom - 1

   For j = bottom To i + 1 Step -1

      If  Then  {#blank#}1{#/blank#}

         t = a(j): a(j) = a(j - 1): a(j - 1) = t

      ElseIf a(j) = a(j - 1) Then    '相邻两个数据相等，进行剔除处理

            {#blank#}2{#/blank#}

         bottom = bottom - 1

      End If

   Next j

   i = i + 1

Loop

Text2.Text = " "

For i = 1 To bottom

   Text2.Text = Text2.Text + Str(a(i))

Next i

End Sub

Private Sub Command2_Click()

Dim i As Integer, j As Integer, tmp As Integer

Dim s1 As String, t As Integer, s2 As String

t=1

For i=1 To n-2

    For j= To n Step 2     ‘改错

        If a(i)*t>a(j)*t Then

            tmp =a(i): a(i)= a(j): a(j)=tmp

        End if

    Next j

                   ‘填空①

Next i

For i =1 To n

    If     Then       ‘填空②

        s1 =s1 Str(a(i))

    Else

        s2=s2+Str(a(i))

    End If

Text2. Text=“奇数位：”+s1

Text3. Text=“偶数位：”+s2

End Sub

回答以下问题：

a(1)="20": a(2)="16": a(3)= "12": a(4)="o": a(5)="k"

For i=1 To 4

    For j=5 To i+1 Step-1

        If a(j)>a(j-1) Then t=a(j):a(j)=a(j-1):a(j-1)=t

    Next j

    List3.AddItem a(i)

Next i

该程序段运行后，列表框List1中显示的内容为（   ）

请回答下列问题：