$re = '/^\(\p{Nd}\)\s+(.+)\n(\(\p{L}\).*?)।\s+Ans\s+\((\p{L})\)/mu';
$str = '(1) Capital of Bangladesh is-
(A) Dhaka (B) Rangpur (C) Chittagong (D) Comilla। Ans (A) Dhaka
(2) Largest city of Bangladesh is-
(A) Mirpur (B) Rangpur (C) Chittagong (D) Comilla। Ans (C) Chittagong
(3) Smallest city of Bangladesh is-
(ক) বাংলা (খ) ইংরেজি । Ans (B) Rangpur';
preg_match_all($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