【单选题】Noise constitutes a real and present danger to people's health. Day and night, at home, at work, and at play, noise can produce serious【C1】______ and psychological stress. No one is【C2】______ to this ...
【简答题】Zinc(锌) is one of about 20 elements necessary for good health. It is present in the body in a very small amount but makes it possible for important chemical actions to be carried out in cells. Scienti...