You are implementing an ASP.NET application that will use session state in out-of-proc mode. You add the following code. public class Person { public string FirstName { get; set;} public string…

You are implementing an ASP.NET application that will use session state in out-of-proc mode. You add the following code. public class Person { public string FirstName { get; set;} public string LastName { get; set;} } You need to add an attribute to the Person class to ensure that you can save an instance to session state. Which attribute should you use?