列表引用问题(疑似 LINQ)

我有一个教学名册，我试图用老师和越位者（来自同一个列表）填补。
如果我直接运行该程序，所有教师和越位者最终都是一样的，尽管他们从不同的方法返回。
如果我暂停程序，观察到创建的任何老师或越位者都将是一个新的、不同的老师。这个问题似乎有类似的内容，这导致我怀疑我误解了 linq 的一个重要部分，以及查询何时完成，但我不明白即使在 2 个函数中也会发生这种情况。
调用代码以及 2 个函数如下所示。感谢您提供的任何见解。

区号：

Teacher T = list.GetTeacher(lesson);
lesson.SetTeacher(T);
lesson.Teacher.AddLesson(lesson);
Teacher O = list.GetOffsider(lesson);
lesson.SetOffsider(O);
lesson.Offsider.AddLesson(lesson);

获取老师：

public Teacher GetTeacher(Lesson lesson)
{
    List<Teacher> Eligible = Teachers.Where(t1 => t1.Active && t1.Styles.Any(ts1 => ts1.Style == lesson.Style.Style && ts1.Level >= lesson.Style.Level)).ToList();
    if (Eligible.Count == 0)
        throw new ArgumentException("Don't have any teachers for that style and/or level");
    List<Teacher> HaventTaught = Eligible.Where(t => !t.DatesTaught.Any(dt => dt.AddDays(21).Day < DateTime.Now.Day)).ToList();
    if (HaventTaught.Count == 0)
    {
        Random r = new Random();
        return Eligible[r.Next(Eligible.Count)];
    }
    else
    {
        Random r = new Random();
        return HaventTaught[r.Next(HaventTaught.Count)];
    }
}

越位者：

public Teacher GetOffsider(Lesson lesson)
{
    if (lesson.Teacher == null)
    {
        throw new ArgumentNullException("Must assign a Teacher to a lesson before an Offsider");
    }
    List<Teacher> Eligible = Teachers.Where(t2 => t2.Active && t2.Styles.Any(ts2 => ts2.Style == lesson.Style.Style && ts2.Level >= lesson.Style.Level)).ToList();
    //remove conflicts of interest
    Eligible = Eligible.Where(t3 => !t3.Avoid.Any(n2 => n2.Equals(lesson.Teacher.Name)) && !lesson.Teacher.Avoid.Any(n4 => n4.Equals(t3.Name))).ToList();
    if (Eligible.Count == 0)
        throw new ArgumentException("Don't have any offsiders for that style and/or level");
    List<Teacher> HaventTaught = Eligible.Where(t4 => !t4.DatesTaught.Any(dt2 => dt2.AddDays(21).Day < DateTime.Now.Day)).ToList();
    if (HaventTaught.Count == 0)
    {
        Random r = new Random();
        return Eligible[r.Next(Eligible.Count)];
    }
    else
    {
        Random r = new Random();
        return HaventTaught[r.Next(HaventTaught.Count)];
    }
}

注意：这两个函数目前都从HaventTeach Lists返回。