21. Salt is manufactured in quantities that exceed those of most, ______, other commercial chemicals. A) of all not B) not if all are C) are not all D) if not all

16. Even at low levels, ______ A) the nervous system has produced detrimental effects by lead. B) lead’s detrimental effects are producing the nervous system. C) lead produces detrimental effects on the nervous system. D) the detrimental effects produced by lead on the nervous system.