void Main()
{
    var allStudents = GetStudents(); 
    var removeList = GetStudents().Where(it=>it.Number<4); //如果1 这边的GetStudents 用allStudents
    
    foreach(var item in removeList)
    {  
        
        bool isRemoved =    allStudents.Remove(item);
        isRemoved.Dump();
    }
    allStudents.Dump();//显示出来看使用提LinqPad
}

public static List<Student> CacheStudents = new List<Student>{new Student(){Number=3,Name="张三"},new Student(){Number=4,Name="李四"},new Student(){Number=5,Name="王五"}};
public List<Student> GetStudents()
{
    //如果2 返回CacheStudents
    return new List<Student>{new Student(){Number=3,Name="张三"},new Student(){Number=4,Name="李四"},new Student(){Number=5,Name="王五"}};
}

public class Student  //如果3 换成 Struct
{
    public int Number
    {get;set;}
    public string Name
    {get;set;}
    
    public override int GetHashCode()
    {
        return Number;
    }
    
    //如果4 重写了Equals
    /*public override bool Equals(object obj)
    {
        return (obj as Student).Number==this.Number;
    }*/
}