You are implementing an ASP.NET application that includes a page named TestPage.aspx. TestPage.aspx uses a master page named TestMaster.master.You add the following code to the TestPage.aspx code-behind file to read a TestMaster.master public property named CityName. Protected Sub Page_Load（ByVal sender As Object，ByVal e As System.EventArgs） Handles Me.LoadDim s As String = Master.CityNameEnd Sub  You need to ensure that TestPage.aspx can access the CityName property. What should you do？（）