31. What does the passage mainly discuss? A) The elements of salt B) The bodies of water of the world C) The many forms of ocean life D) The salinity of ocean water

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.