如何从控制器指定返回视图？

That's the controller I have:

那是我的控制器:

public ActionResult LabPreparation(int? id)
{
    if (id == null) return new HttpNotFoundResult();

    var lab = db.Labs.Find(id);
    if (lab == null) return HttpNotFound();

    return View(lab);
}
publ