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小明设计了某社团积分系统，当输入用户ID和积分增值后可以更新积分和排名。具体功能如下：单击“读取”按钮Commandl后，将n个用户的ID（依次为1到n）、积分和积分排名显示在列表框List1中。在Text1中输入ID和积分增值，用逗号作为分隔符和结束符，奇数位置整数表示ID，偶数位置整数表示积分增值。如输入“2,1,3,5，”表示ID为2的用户增加1积分，ID为3的用户增加5积分。单击“更新”按钮Command2，在列表框List2中显示更新后的积分和排名。程序运行界面如图所示。

请回答下列问题：

（1）若要清空列表框 List1，下列代码正确的是______(单选，填字母：A.List1.Clear / B.List1.Caption="" / C.List1.Text="" )。
（2）实现上述功能的 VB 程序如下，请在划线处填入合适的代码。
（3）程序中加框处代码有错，请改正

Const n = 12

Dim a(1 To n) As Integer, mc(1 To n) As Integer

Private Sub Command1_Click()

   ’n个用户的ID依次为1到n,读取n个用户的积分和排名数据分别存储到数组a和数组mc中，并在列表框List1中显示ID、积分、积分排名，代码略

End Sub

Private Sub Command2_Click()

     Dim i As Integer, j As Integer, k As Integer, d As Integer

     Dim s As String, flag As Boolean, x As Integer, y As Integer

     Dim p(1 To 20) As Integer   '存储输入的ID和积分增值，每次输入不超过10组

     For i = 1 To 20

          p(i) = 0

     Next i

     s = Text1.Text

     __________①          

     d = 0: k = 0

     For i = 1 To Len(s)

          If Mid(s, i, 1) = "," Then

             If flag Then

                 x = Val(Mid(s, i - d, d))

                 For j = 1 To k Step 2

                      If p(j) = x Then Exit For

                 Next j

                 If j > k Then

                      p(j) = x: k = k + 2

                 End If

             Else

                 y = Val(Mid(s, i - d, d))

                 p(j + 1) = p(j + 1) + y

             End If

             flag = Not flag:   d = 0

          Else

             ______②       

          End If

     Next i

     For i = 1 To k \ 2

             x = p(2 * i - 1): y = p(2 * i)

             mc(x) = 1

             For j = 1 To n

                 If j <> x Then

                         If a(j) < a(x) + y And a(j) >= a(x) Then___________

                 End If

                 If a(j) > a(x) + y Then mc(x) = mc(x) + 1

             Next j

             ________③       

     Next i

     '在列表框List2中显示ID，积分、排名，代码略

End Sub