Web service return string in JSON format

How to return string JSON format in webservice?

currently shown:

<?xml version="1.0" encoding="utf-8"?>
<string xmlns="http://example.net/ws1/">[
{
    "name":"John"
},
{
    "name":"Susan,
}

]

how to get rid: - - - at the end of the result..?

    [WebMethod(Description = "Show Policy Info")]
    [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
    public string showInfo()
    {
        List<oInfo> lst = new List<oInfo>();
        oInfo pi = new oInfo();
        lst.name = "Mike";
        lst.Add(pi);
        lst.name = "John";
        lst.Add(pi);
        lst.name = "Susan";
        lst.Add(pi);
        return JsonConvert.SerializeObject(lst);
     }

     public class oInfo
     {
         public string name { get; set; }
     }