$re = '/\.\s+(Nature and purpose of financial analysis|Users and decision making)\s+(?:An|We)/';
$str = '"As discussed in chapter 1, the users of financial statements can be categorised as resource provider. Users and decision making An example for this. Nature and purpose of financial analysis We have identi fied that financial analysis mvolves expressing reported numbers in financial statements in relative terms. "';
$subst = "\n";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php