Нужно присвоить значение ключа к переменной

private void button6_Click(object sender, EventArgs e)
        {
            IWebElement text = Browser.FindElement(By.TagName("pre"));
            string textt = text.Text;
            Root? r = JsonConvert.DeserializeObject<Root>(textt);
            string? Tradeofferid = 
            string? Assetid = 
        }

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace Test
{
 
    public class Root
    {
        public Response response { get; set; }
    }
 
    public class Response
    {
        public Trade_Offers_Received[] trade_offers_received { get; set; }
        public int next_cursor { get; set; }
    }
 
    public class Trade_Offers_Received
    {
        public string tradeofferid { get; set; }
        public int accountid_other { get; set; }
        public string message { get; set; }
        public int expiration_time { get; set; }
        public int trade_offer_state { get; set; }
        public Items_To_Give[] items_to_give { get; set; }
        public bool is_our_offer { get; set; }
        public int time_created { get; set; }
        public int time_updated { get; set; }
        public bool from_real_time_trade { get; set; }
        public int escrow_end_date { get; set; }
        public int confirmation_method { get; set; }
    }
 
    public class Items_To_Give
    {
        public int appid { get; set; }
        public string contextid { get; set; }
        public string assetid { get; set; }
        public string classid { get; set; }
        public string instanceid { get; set; }
        public string amount { get; set; }
        public bool missing { get; set; }
        public string est_usd { get; set; }
    }
 
}

string Tradeofferid = r.response.trade_offers_received.FirstOrDefault().tradeofferid;
 
string Assetid = r.response.trade_offers_received.FirstOrDefault().items_to_give.FirstOrDefault().assetid;

for (int i = 0; i < r.response.trade_offers_received.Length; i++)
{
    Tradeofferid = r.response.trade_offers_received[i].tradeofferid;
    for (int j = 0; j < r.response.trade_offers_received[i].items_to_give.Length; j++)
    {
        Assetid = r.response.trade_offers_received[i].items_to_give[j].assetid;
    }
}