在preg_replace中用array替换字符串

I have a string which I want to filter. I want to find some words which I want to replace using preg_replace. My parameters are an array of words I want to take out from my string, and my replacements is just an empty space. Can someone please help me to solve this problem.

My Code:

$str = "Hello world. It's a beautiful day.";
$para = array("world","day");
$newstr = preg_replace('/\b($para)\b/','',$str);
echo $newstr;

You can use it like this:

$str = "Hello world. It's a beautiful day.";
$para = array("/world/","/day/");
$newstr = preg_replace($para,'',$str);
echo $newstr;

Regex can't be an array but first parameter of preg_replace can be an array of regexes, you have to do:

$para = array("/\bworld\b/", "/\bday\b/");
$newstr = preg_replace($para, '', $str);

I've added word boundary arround the words, for not matching words like daily