"it" 是做形式宾语:
(1) 答案是 A: it ("it" 代前面的 "being a parent ..." =
(2) "them" 肯定错, 因为"a parent/parent" = 单数!
(3) "one" : ; 指父/母; 也是错误的. 因为句子前面的"being"不是指人(父/母), 而是指
(4) "him" 指父...也错!
(5) 改写句子你会更理解:
(i) ... and (= it) often carries extra stress for those who are the parent of a child with special needs.
(ii)... and