The defence lawyer was questioning the old man who was one of the________of the murder

committed last month.[      ]

A. observers  

B. viewers

C. witnesses  

D. audiences

生活饮用水水质标准（CJ3020—1993）规定一级水源水氨氮（以氮计）的含量为不得超过（）。

A、1.0mg/L

B、0.1mg/L

C、0.5mg/L

D、0.05mg/L