public string ToString(string format, IFormatProvider formatProvider)
{
    // 'n': print the name only.
    if (format == "n")
    {
        return Name;
    }

    // 'cl': print the course list.
    if (format == "cl")
    {
        string stringFormat = "{0,-25}{1,-30}{2,-10}\r\n";

        StringBuilder str = new StringBuilder();

        str.AppendLine(); 
        str.AppendFormat(stringFormat, "Title", "Description", "ID");
        str.AppendLine(); 

        foreach (Course c in Courses)
        {
            str.AppendFormat(stringFormat, c.Title, c.Description, c.SectionID);
        }

        return str.ToString();
    }

    return this.ToString();
}