From a list of words, we want to find what word occurrs first inside a given input string.
Solution
$arrWords = array("one", "two", "three");
$strInput = "Test a paragraph three and testing some more one test test two";
function getFirstOccurrence($strInput, $arrWords) {
	$arrInput = explode(" ", $strInput);
	foreach($arrInput as $strInput) {
		if(in_array($strInput, $arrWords)) {
			return $strInput;
		}
	}
	return null;
}
print "First word is: " . getFirstOccurrence($strInput, $arrWords);