How to return 2 dropdowns simultaneously in MVC view

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using WebApplication10.Models;

namespace WebApplication10.Controllers
{
    
    public class userdataController : Controller
    {
        // GET: userdata
        public ActionResult userdata()
        {
         
           userdata model = new userdata
             {
                model.environmentlist = new List<string> { "w1", "w2", "w3", "w4" };
        };
            return View(model);


        }

           
        
        [HttpPost]
        public ActionResult userdata(userdata model)
        {

            if (string.IsNullOrEmpty(model.unumber))
            {
                model.ValidationMsg = "Please enter unumber";

            }

            else
            {
                switch (model.envoption)
                {

                    case "w1":
                        switch(model.regionoption)
                        {
                            case "us1":

                                break;
                            case "us2":
                                break;

                            case "us3":
                                break;

                        }
                        break;
                      
                    case "w2":
                        switch (model.regionoption)
                        {
                            case "us1":

                                break;
                            case "us2":
                                break;

                            case "us3":
                                break;
                        }
                        break;
                    case "w3":
                        switch (model.regionoption)
                        {
                            case "us1":

                                break;
                            case "us2":
                                break;

                            case "us3":
                                break;

                        }
                        break;

                    case "w4":
                        switch (model.regionoption)
                        {
                            case "us1":
                                break;

                              
                            case "us2":
                                break;

                            case "us3":
                                break;

                        }
                        break;
                }

            }

          model.environmentlist = new List<string> { "w1", "w2", "w3", "w4" };
            model.region= new List<string> { "us1", "us2", "us3" };
            return View(model);

        }

    }

}