<!DOCTYPE HTML>
<html lang="es-MX">
  <head>
    <title>
      Curso PHP - Uso de comillas en PHP
    </title>
  </head>
  <body style="background-image:url('images/logoBG.jpg');">
    <?php
      $Str = "Mi String";
      $Preg1 = "Cual es $Str<br />";
      $Preg2 = 'Cual es $Str<br />';

      echo( "<p>" );
      echo     $Preg1;
      echo     $Preg2;
      echo( "</p>" );
    ?>
  </body>
</html>