Question from the HTML5/CSS3 test

Among the techniques presented below, which ones are said to be "non-blocking"?

<!-- Technique 1 -->
<script src="example.js" type="text/javascript"></script>
 
<!-- Technique 2 -->
<script src="example.js"></script>
 
<!-- Technique 3 -->
<script src="example.js" async></script>
 
<!-- Technique 4 -->
<script type="text/javascript">
    document.write('<script src="example.js" type="text/javascript"></scr'+'ipt>');
</script>
 
<!-- Technique 5 -->
<script type="text/javascript">
    var script = document.createElement('script');
    script.src = 'example.js';
    script.type = 'text/javascript';
    document.getElementsByTagName('script')[0].parentNode.appendChild(script);
</script>