PHP：为下拉菜单句柄注入选择查询

How can I improve this code to make it handle injection and inputs with quotes?

$result = $conn->query("select bookName from Book");

echo "<select name='bookName'>";

while ($row = $result->fetch_assoc()) {
  unset($bookName);
  $bookName = $row['bookName'];
  echo '<option value="'.$bookName.'">'.$bookName.'</option>';
}