数组到字符串的转换-关联数组

我使用下面的代码来解析一个问题及其选择。

$entries = preg_split('/(?=[a-z'd]+'.(?!'d))/', $str, -1, PREG_SPLIT_NO_EMPTY);
$arrAnswers = array();
$arrQuestions = array();
$id = 0; //Assuming your table is empty
foreach($entries as $entry) { //Loop through the grabbed records
  if(is_numeric(substr($entry, 0, 1)) === true) { //Is it a question?
     $id++;     
     $arrAnswers[$id] = array();
     $arrQuestions[$id] = '('''. $entry .''')'; 
  } else { //Ok, it's a possible answer to a question
     $arrAnswers[$id][] = '('''. $entry .''', '. $id .', 0)';
  }
}
      echo "<pre>";
        print_r($arrQuestions);
      echo "<pre>";
      echo "<br>";
      echo "<pre>";
        print_r($arrAnswers);
      echo "<pre>";

返回以下数组结果：

$arrQuestions output
Array
    (
        [1] => ('1. What is foo?')
        [2] => ('2. What is foo?')
    )
$arrAnswers output
    Array
    (
        [1] => Array
            (
                [0] => ('a. foo1', 1, 0)
                [1] => ('b. foo2', 1, 0)
                [2] => ('c. foo3', 1, 0)
                [3] => ('d. foo4', 1, 0)
            )
        [2] => Array
            (
                [0] => ('a. foo1', 2, 0)
                [1] => ('b. foo2', 2, 0)
                [2] => ('c. foo3', 2, 0)
                [3] => ('d. foo4', 2, 0)
            )
    )

我插入记录的代码：

try {
$conn = new PDO("mysql:host=$servername;dbname=$dbname", $username, $password);
// set the PDO error mode to exception
$conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$strDbQuery = "INSERT INTO `question` (`q_name`) VALUES ". implode(", ", $arrQuestions);
$strDbQuery_2 = "INSERT INTO `answers` (`choices`, `question`, `correct`) VALUES ". implode(", ", $arrAnswers);
// use exec() because no results are returned
$conn->exec($strDbQuery);
$conn->exec($strDbQuery_2);
echo "New questions uploaded successfully";
}
catch(PDOException $e)
{
echo $strDbQuery . "<br>" . $e->getMessage();
echo $strDbQuery_2 . "<br>" . $e->getMessage();
}
$conn = null;

我打印了事务的消息，在插入答案时，插入的值是一个数组。我使用了函数implode()，但它仍然被视为一个数组。

INSERT INTO `question` (`q_name`) VALUES ('1. What is foo1?'), ('2. What is foo2?')  
INSERT INTO `answers` (`choices`, `question`, `correct`) VALUES Array, Array

伙计们，我该怎么办？