How to learn what tech used for a web ?

Hi all,

How can we learn what tech used to build a website, in case extension is hidden?

For ex, it’s usually a link like that: news.php?cat=1&sub=2&id=3

Now, it’s turned to news.abc?cat=1&sub=2&id=3

How can I know developers use PHP or ASP or JSP…?

Thanks,

Me2min