C#Rest API返回动态对象

WebServiceHost webServiceHost= new WebServiceHost(typeof(WebMethods),new Uri(url));
webServiceHost.Open();

public class Fish { public string name = "I am a fish"; }
public class Dog { public int legs = 4; }
public class Cat { public DateTime dt = DateTime.Now;}

我的一个webMethods应该返回一个动态对象

的WebMethod：

解决方案1

[OperationBehavior]
[WebGet(ResponseFormat = WebMessageFormat.Json,UriTemplate = "/isTest?class={cl}")]
object isTest(string cl)
{
    object obj;

    switch (cl)
    {
        case "fish":
            obj= new Fish();
            break;
        case "dog":
            obj= new Dog();
            break;
        default:
            obj= new Cat();
            break;

    }
    return obj;

}

解决方案2

[OperationBehavior]
[WebGet(ResponseFormat = WebMessageFormat.Json,UriTemplate = "/isTest?class={cl}")]
dynamic isTest(string cl)
{
    dynamic obj;

    switch (cl)
    {
        case "fish":
            obj= new Fish();
            break;
        case "dog":
            obj= new Dog();
            break;
        default:
            obj= new Cat();
            break;

    }
    return obj;
}

两者都不起作用.响应是ERR_CONNECTION_RESET

知道如何实现它吗？
感谢帮助.