从C访问json节点时出现问题#

我有一个json文件需要保存为sqlserver表。这是测试.json有学生详细资料的课程。

[{
    "Studentid": "001006360",
    "Grade": "2",
    "ExtraWork": {
        "TopRecommended": ["000133692",
        "102067155",
        "887273865"],
        "OtherCourses": ["228963647",
        "138909237",
        "899791144",
        "216165613",
        "113239563"]
    },
    "Courses": [{
        "smalldesc": "this is a test ",
        "Details": {
            "description": "Summary of the course",
            "collegeCode": "32466"
        }
    },
    {
        "smalldesc": "Second test",
        "Details": {
            "description": "Business- Course Summary",
            "collegeCode": "32469"
        }
    }]
}]

下面是C程序。 我不知道如何访问“smalldesc”和“collegeCode”。

var jsonText = File.ReadAllText(@"C:\test.json");    
var ser = JsonConvert.DeserializeObject<List<RootObject>>(jsonText);
for (int i = 0; i < ser.Count; i++)
{
    string Studentid = ser[i].Studentid;
    string  Grade = ser[i].Grade;

    var result = JsonConvert.DeserializeObject<List<Course>>(jsonText);
    for (int k = 0; k < result.Count; k++)
    {
        string smalldesc = result[k].smalldesc;
        string collegeCode = result[k].Details.collegeCode;
    }
}

Json对象类定义:

public class ExtraWork
{
    public List<string> TopRecommended { get; set; }
    public List<string> OtherCourses { get; set; }
}

public class Details
{
    public string description { get; set; }
    public string collegeCode { get; set; }
}

public class Course
{
    public string smalldesc { get; set; }
    public Details Details { get; set; }
}

public class RootObject
{
    public string Studentid { get; set; }
    public string Grade { get; set; }
    public ExtraWork ExtraWork { get; set; }
    public List<Course> Courses { get; set; }
}