SDK获取审批数据怎么返回json格式的？

默认都是返回XML格式，怎么配置 format=json  ？？ 谢谢


IDingTalkClient client = new DefaultDingTalkClient('https://eco.taobao.com/router/rest]ttps://eco.taobao.com/router/rest');
SmartworkBpmsProcessinstanceListRequest req = new SmartworkBpmsProcessinstanceListRequest();
req.ProcessCode = "PROC-FF6YR2IQO2-NP3LJ1J0SO4182NKX26K3-3N23J-PB";
req.StartTime = 1496678400000L;
req.EndTime = 1496678400000L;
req.Size = 10L;
req.Cursor = 0L;
SmartworkBpmsProcessinstanceListResponse rsp = client.Execute(req, access_token);
Console.WriteLine(rsp.Body);