Решение:
1) a father — d. a mother or father
2) a parent — d. a mother or father
3) a stepmother — a. the woman who is married to someone’s biological parent but who is not their biological mother
4) a brother-in-law — b. the husband of your sister or brother, or the brother of your husband or wife, or the man who is married to the sister or brother of your wife or husband
Итак, правильные соответствия:
1) a father — d
2) a parent — d
3) a stepmother — a
4) a brother-in-law — b