19. Seldom______ games been of practical use in playing real games. A) theories of mathematics B) theorized as mathematics C) has the mathematical theory of D) the mathematical theory has

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.