PHP - exec（）方法不执行

I am experiencing problems running the following PHP code:

Get_Words_And_Display.php:

    <?php
  require('Database.php');

      $word_w = $_POST['word'];
        $word_def = $_POST['def'];
        $word_cat = substr($word_w, 0, 1);

        $SQLQueryIns = "INSERT INTO all_words (Category, Words, Definition) VALUES ('$word_cat', '$word_w', '$word_def')";
        $MySQL_db->exec($SQLQueryIns); //PDO Object is assigned to $MySQL_db

        $SQLQueryGet = "SELECT * FROM all_words";
        $SQLGet = $MySQL_db->query($SQLQueryGet);/*Each value is displayed in a table using foreach*/ ?>

Here is what I want the application to do:
1) User enters values in Create_Word.php
2) Create_Word.php POSTS the values to Get_Words_And_Display.php
3) Get_Words_And_Display.php processes values and displays the values

However the POST values from Create_Word.php is not displayed (There are no errors).
My Database works completely fine, it's just the Get_Words_And_Display.php.
What am I doing wrong here?

Here is the Create_Word.php file:

                      <form action="Get_Words_And_Display.php" method="POST">
                    <div style="border-top:dotted; border-width:2px; margin-top: 10px; padding-top: 20px;">
                       <p>
                            <label for="word">Word:</label>
                            <input type="text" name="word" />
                         </p>                      
                         <p>
                            <label for="definition">Definition:</label>
                            <textarea name="def"></textarea>
                         </p>
                         <input type="submit" />
                        </div>
                  </form>

My foreach code in located within the Get_Words_And_Display.php file:

                <?php foreach($SQLGet as $AllResults) : ?>
                   <tr>
                        <td class="dataCell"><?php echo $AllResults['Category']; ?></td>
                      <td class="dataCell"><?php echo $AllResults['Word']; ?></td>
                      <td class="definition"><?php echo $AllResults['Definition']; ?></td>
                     </tr>
                <?php endforeach; ?>