$re = '/(?P<q_num>\d{1,3})\)\s?(?P<quest>.+)\n
(\s?a\)\s?)(?P<ans_a>(?:(?![a-d]\)).)+)
(b\)\s?)(?P<ans_b>(?:(?![a-d]\)).)+)
((c\)\s?)(?P<ans_c>(?:(?![a-d]\)).)+))?
((d\)\s?)(?P<ans_d>(?:(?![a-d]\)).)+))?/x';
$str = '1) First question with 4 choices ?
a) First choice b) Second choice c) Third choice d) Last choice
2) Second question with only 3 choices ?
a) First choice b) Second choice c) Last choice
3) True or False ?
a) True b) False';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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