The select tag does not appear if I import the contents of the other page, only if I put it directly into the index. Here is the code:
index.php
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Cadastro de Carros!</title>
<link href="https://fonts.googleapis.com/icon?family=Material+Icons" rel="stylesheet">
<link type="text/css" rel="stylesheet" href="css/materialize.css">
<meta name="viewport" content="width=device-width, initial-scale=1.0"/>
</head>
<body class="light-green lighten-5">
<!-- NAVBAR -->
<br />
<div class="conteudo" id="conteudo">
**<?php include 'controle.php' ?>**
</div>
<!--Revisar Footer -->
<!--?php include 'footer.php' ?-->
<script type="text/javascript" src="https://code.jquery.com/jquery-3.2.1.min.js"></script><scripttype="text/javascript" src="js/materialize.min.js"></script>
<script type="text/javascript" src="js/js.js"></script>
</body>
</html>control.php
<br />
<br />
<br />
<br />
<div class="container white">
<div class="row">
<form class="col s12">
<div class="row">
<div class="input-field col s6">
<input id="placa" type="text" class="validate">
<label for="placa">Placa</label>
</div>
<div class="input-field col s6">
<input id="adesivo" type="number" class="validate">
<label for="adesivo">Nº do adesivo</label>
</div>
</div>
<div class="row">
<div class="input-field col s6">
<select>
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="mercedes">Mercedes</option>
<option value="audi">Audi</option>
</select>
</div>
<div class="input-field col s6">
<input id="placa" type="text" class="validate">
<label for="placa">Placa</label>
</div>
</div>
</div>
</form>
</div>
</div>