这个XML文件的类结构可能是什么？

Question

我想通过C＃序列化创建一个类似上面的XML文件，这个文件的类结构是什么？这样它会在序列化后生成所需的XML文件。

<Subjects>
    <Subject>Maths</Subject>
    <Questions>
        <Question>Maths question 1</Question>
        <Answer>Maths answer 1</Answer>
        <Marks>10</Marks>
    </Questions>
    <Questions>
        <Question>Maths question 2</Question>
        <Answer>Maths answer 2</Answer>
        <Marks>5</Marks>
    </Questions>
    <Questions>
        <Question>Maths question 3</Question>
        <Answer>Maths answer 3</Answer>
        <Marks>20</Marks>
    </Questions>
</Subjects>
<Subjects>
    <Subject>Science</Subject>
    <Questions>
        <Question>Science question 1</Question>
        <Answer>Science answer 3</Answer>
        <Marks>20</Marks>
    </Questions>
    <Questions>
        <Question>Science question 2</Question>
        <Answer>Science answer 3</Answer>
        <Marks>10</Marks>
    </Questions>
    <Questions>
        <Question>Science question 3</Question>
        <Answer>Science answer 3</Answer>
        <Marks>20</Marks>
    </Questions>
</Subjects>

我正在尝试使用这个类结构 -

 public class Subjects
    {
        public string Subject
        {
            get; set;
        }
        public List<Questions> Questions
        {
            get; set;
        }
    }

    public class Questions
    {
        public string Question
        {
            get; set;
        }
        public string Answer
        {
            get; set;
        }
        public string Marks
        {
            get; set;
        }
    }

但是在使用序列化后它没有生成所需的XML文件 XMLSerializer的。