VBA 过程转写函数 不知道哪里出错了，帮忙看看！谢谢

一叶一沙

在sheet2中：
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim a As String, b As String, c As Single
a = Range("a3").Value
a = Format(a, "m月d日")
b = Range("b3").Value

     ThisWorkbook.Sheets(1).Select
    With Sheets(1).Cells
        .AutoFilter Field:=1, Criteria1:=a
        .AutoFilter Field:=2, Criteria1:=b
         c = Application.WorksheetFunction.Subtotal(9, .Range("C:C"))
        .AutoFilter
    End With

MsgBox (c)

Range("c3") = c
End Sub

在模块2中：
Function bree(a As String, b As String) As Single
a = Format(a, "m月d日")
     ThisWorkbook.Sheets(1).Select
    With Sheets(1).Cells
        .AutoFilter Field:=1, Criteria1:="a"
        .AutoFilter Field:=2, Criteria1:="b"
        c = Application.WorksheetFunction.Subtotal(9, .Range("C:C"))
        .AutoFilter
    End With
bree = c
End Function

一叶一沙

sub过程可以运行的，想设置成函数，方便使用，就是不行，唉！