在窗体上画1个名为Text1的文本框和1个名为Label1的标签，再画4个名为Op1的单选按钮控件数组，其Index属性按季度顺序为0～3，如图1所示。在文件Sales.txt中按月份顺序存有某企业某年12个月的销售额。要求在程序执行时，鼠标单击一个单选按钮，则Text1中显示相应季度的销售总额，并把相应的文字显示在标签上。如图2所示是单击“第二季度”单选按钮所产生的结果。请选择可在空白处填写的合适语句( )。
Option Base 1
Dim sales(12) As Long
Private Sub Form_Load()
Open "c:\sales.txt" For Input As #1
Fork= 1 To 12
Input #1, sales(k)
Next k
Close #1
End Sub
Private Sub ______ (Index As Integer)
Dim sum As Long, k As Integer, month As Integer
sum=0
month=Index*
Fork=1 To 3
month=month+1
sum=sum+sales(month)
Next k
Label1. Caption=______.Caption & "销售总额:"
Text 1=sum
End Sub
A．Op1_Click3 Op1 (Index)
B．Op1_Click0 Option1 (Index)
C．Option1_Cliek 1 Op1 (Index)
D．Option1_Click 2 Option1 (Index)
