我的php文件只是在我提交表单时显示代码

Question

因此，每次我提交表单时，它只显示我的PHP代码，我尝试查找其他主题，但我没有找到我的问题的答案，这是我的HTML代码

<form action="contactus.php" method="post">
<div  class="form-group">
    <label for="Subject">Subject*</label>
    <input name="subject" class="form-control" id="subject1" placeholder="Subject">
</div>
<label for="sabject">Why do you want to contact us?</label>
    <br>
    <select name="select">

        <option value="General Inquiry">General Inquiry</option>
        <option value="hampion Guide Request">Champion Guide Request</option>
        <option value="League of Legends Show(s) Request">League of Legends Show(s) Request</option>
        <option value="Podcast - League of Legends">Podcast - League of Legends</option>
    </select>
    <label for="fname">First Name*</label>
    <input type="text" name="firstname" class="form-control" id="namef" placeholder="First Name">

    <label for="lname">Last Name</label>
    <input type="text" name="lastname" class="form-control" id="namel" placeholder="Last Name">
    <label for="email_adress">Email Adress*</label>
    <input type="email" name="email_adress" class="form-control" id="email_adress" placeholder="Email Adress">
    <label for="message">Message*</label>
    <input name="message2" class="form-control" id="message" placeholder="message">
    <input style="margin-top: 50px;" value="Send Form" name="submit" type="submit">Submit</button>
</form>

这是我的PHP代码

<?php
$to ="sudaiguy1@gmail.com";
$from = $_POST['email_adress'];
$email_subject = $_POST['subject'];
$subject = "your subject here"
$message = $_POST['select'];
$message2 = $_POST['message2'];
$name = $_POST['firstname'];
if (empty($name)||empty($from))
{
    echo "Name and email are mandatory!";
    exit;
}
elseif (empty($email_subject)||empty($message)) {
    echo "Your email or subject are blank, please write something in them";
    exit;
}
elseif (empty($name)||empty($message2)) {
    echo "Your name or message are empty";
    exit;
}
$name2 = $_POST['lastname'];
$email_from = "sudaiguy1@gmail.com";
$email_body = $_POST['You have been contacted by $name $name2 and his email is $from. \n The message he wanted to say was in the subject of $message and the message is $message2'];
$headers = "From: $email_body"
mail($to,$email_subject,$email_body,$headers);
if($sent) {
    print ("You have successfully submitted it."); 
}
else {
    print ("We have encountered an error sending your message, please try again.");
}
?>

我尝试过多种方法，告诉我你是否需要更多信息