您在第一个循环中覆盖您的变量...以下是：

You overwrite your variables in the first loop... Take this:

$answer = isset($_POST['answer']) ? $_POST['answer'] : "" ;
$fraction = isset($_POST['fraction']) ? $_POST['fraction'] : "" ;
$feedback = isset($_POST['feedback']) ? $_POST['feedback'] : "" ;

foreach($answer as $key=>$value){
    $query = "insert into `question_answer` ( answer, fraction, feedback) values ('$value', '$fraction[$key]','$feedback[$key]')";
    $questions->insertData($query,$con);
}