我正在尝试通过pdo插入mysql表。当我运行代码时，我得到错误：column not found:1054 unknown column'testing'in'field list'when using testing as the first input for the first row in the html code below`

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);
    $sql = "INSERT INTO test (Name, Test)  VALUES ($first, $Test)";

    $conn->exec($sql);
    echo "New record created successfully";
    }
catch(PDOException $e)
    {
    echo $sql . "<br>" . $e->getMessage();
    }

$conn = null;
?>

<table width="300" border="0" align="center" cellpadding="0" cellspacing="1">
<tr>
<td><form name="form1" method="post" action="page_ac.php">
<table width="100%" border="0" cellspacing="1" cellpadding="3">
<tr>
<td colspan="3"><strong>Test </strong></td>
</tr>
<tr>
<td width="71">Name</td>
<td width="6">:</td>
<td width="301"><input name="name" type="text" id="name"></td>
</tr>
<tr>
<td>test</td>
<td>:</td>
<td><input name="Test" type="text" id="Test"></td>
</tr>
<tr>
<td colspan="3" align="center"><input type="submit" name="Submit" value="Submit"></td>

</tr>
</table>
</form>
</td>
</tr>
</table>