Returning TWO Lists using JSON and Serializer

I'm sending a List from my ASP.NET WebMethod to my Javascript using this:

List<Person> plist = new List<Person>();

string json = "";
System.Web.Script.Serialization.JavaScriptSerializer oSerializer = new System.Web.Script.Serialization.JavaScriptSerializer();
json = oSerializer.Serialize(plist );

return json;

And I'm using this to retrieve these values from my JS:

function onSuccess(val) {
        var obj = JSON.parse(val)
        obj.forEach(function (entry) {
               console.log(entry);
       });
}

Everything works well. However now I want to return TWO lists such as:

List<Person> plist = new List<Person>();
List<Car> carlist = new List<Car>();

using the same mechanism I used before. How can I insert two lists to the Serializer and print them from my JS?