why the function "htmlentities" doesn't work?

[seahorse123]

I found that the function "htmlentities" doesn't work on my server, for example I have the code:

<?php
$str = "A 'quote' is <b>bold</b>";
echo htmlentities($str, ENT_QUOTES);
?>

it's supposed to display:
A 'quote' is <b>bold</b>
but what I can see is:
A 'quote' is <b>bold</b>

I don't know why the function "htmlentities" doesn't work, some other functions like "htmlspecialchars()" also doesn't work, anyone knows the reason? thanks.

 

[seahorse123]

I have figured it out, it does convert but cannot be shown on the browser.