$re = '/(?mi)(\d+)\.\h+(.+)(?:\R[a-e]\.\h+(.+))?(?:\R[a-e]\.\h+(.+))?(?:\R[a-e]\.\h+(.+))?(?:\R[a-e]\.\h+(.+))?(?:\R[a-e]\.\h+(.+))?\RAns:\h+(.+)/u';
$str = '1. Question with 4 choices
a. one a
b. one b
c. one c
d. one d
Ans: B
23. True-False Question with no choices
Ans: T
2. Question with 3 choices
a. two a
b. two b
c. two c
Ans: C
3. Question with 2 choices
a. three a
b. three b
Ans: B';
preg_match_all($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