访问<；选择>；元素

我正在尝试创建一个简单的表单，在提交表单时将数据发送到PHP脚本。我能够访问所有的文本框值，并成功实现了每个值的变量。然而，当我试图访问表单上组合框的值时，我在PHP:中得到了这个错误

注意：第15行C:''inetpub''wwwroot''krAssignment4''scripts''index.php中的未定义索引：cmbProvince

HTML

<form id="orderForm" action="scripts/index.php" method="post" onsubmit="return validateForm()">
        <fieldset id="customerInfo">
            <legend>Customer Information</legend>
            <label for="txtFirstName">Name:</label><br>
            <input type="text" id="txtFirstName" name="txtFirstName"
                   placeholder="First Name" autofocus="true"
                   oninput="formatFirstName()">
            <input type="text" id="txtLastName" name="txtLastName"
                   placeholder="Last Name" oninput="formatLastName()"><br><br>
            <label for="txtAddress">Address:</label><br>
            <input type="text" id="txtAddress" name="txtAddress" placeholder="Address"
                   oninput="formatAddress()"><br>
            <input type="text" id="txtCity" name="txtCity" placeholder="City"
                   oninput="formatCity()">
            <select id="cmbProvince" name="cmbProvince">
                <option value="on">ON</option>
                <option value="qc">QC</option>
                <option value="mb">MB</option>
                <option value="sk">SK</option>
                <option value="ab">AB</option>
                <option value="bc">BC</option>
                <option value="nb">NB</option>
                <option value="nl">NL</option>
                <option value="ns">NS</option>
                <option value="nu">NU</option>
                <option value="pe">PE</option>
                <option value="nt">NT</option>
                <option value="yt">YT</option>
            </select><br>
            <input type="text" id="txtPostalCode" name="txtPostalCode"
                   placeholder="Postal Code" oninput="displayPostalCode()">
            <br><br>
            <!-- Button that will display the order form -->
            <input type="button" id="btnOrder" value="Order"
                   onclick="showOrderInformation()">
        </fieldset><br>
        <fieldset id="orderInfo">
            <legend>Order Information</legend>
            <label for="cmbProduct">Product:</label><br>
            <select id="cmbProduct">
                <option> -- Select -- </option>
                <option>Blackberries</option>
            </select>
            &ensp;@&ensp;
            <input type="number" id="txtQuantity" name="txtQuantity" value="1"
                   step="1" min="1" max="50" oninput="displayTotalTax()"><br><br>
        </fieldset>
        <br><br>
        <!-- Button to submit the form to PHP after validation -->
        <input type="submit" id="btnSubmit" value="Submit">
    </form>

PHP（第10-19行）

/* Capture the user input from the HTML form */
$strFirstName = $_POST['txtFirstName'];
$strLastName = $_POST['txtLastName'];
$strAddress = $_POST['txtAddress'];
$strCity = $_POST['txtCity'];
$strProvince = $_POST['cmbProvince'];
$strPostalCode = $_POST['txtPostalCode'];

我打字有问题吗？还是错过了什么？除组合框外的所有都在工作。

如果我需要包括其他内容，请告诉我。谢谢

编辑

以下是当我尝试var_dump($_POST);:时会发生的情况

Notice: Undefined index: cmbProvince in C:'inetpub'wwwroot'krAssignment4'scripts'index.php on line 15 
Notice: Undefined index: cmbProduct in C:'inetpub'wwwroot'krAssignment4'scripts'index.php on line 18 
array(6) { ["txtFirstName"]=> string(7) "Kendall" 
["txtLastName"]=> string(4) "Roth" 
["txtAddress"]=> string(19) "22 Resolution Drive" 
["txtCity"]=> string(8) "Millbank" 
["txtPostalCode"]=> string(7) "K2K 2K2" 
["txtQuantity"]=> string(1) "2" }