function get_Materials_by_grade_and_subject_and_category($grade_id, $subject_id, $cat)
{
    $My_DB = new My_Database();
    $found = "";
    if (isset($My_DB->get_materials_by_grade_and_subject_and_category($grade_id, $subject_id, $cat)['result'])) {
        $Materials = $My_DB->get_materials_by_grade_and_subject_and_category($grade_id, $subject_id, $cat)['result'];
        foreach ($Materials as $material) {
            $file_path = '../private/videos/' . $material['file_name'];
            $bb = '?page=p_gallery&file_path=' . $file_path . '&grade=' . $material['grade_id'] . '&subject=' . $material['subject_id'];
            $found = $found . '<li><a href=' . $bb . '>' . $material['name'] . '</a> </li>';
        }
        $found = '<ul>' . $found . '</ul>';
    }
    return $found;
}