Name of calling procedure

If a procedure A calls another procedure B, can I get the name of procedure A in proc B?
In below example, I am looking for piece of code to replace "??????", so that it should return either a or c

Private Sub a()
    Call b
End Sub


Private Sub c()
    Call b
End Sub

Private Sub b()
    MsgBox "called by " & ??????
End Sub

Thanks
ajay