一般认为，水体中总磷为（），无机氮（）以上就会出现富营养化。
参考答案：0.02mg/L；0.3mg/L
Environmentalists urged that more effective measures ___________by the government to reduce the pollution.
A．were taken
B．would adopt
C．be adopted
D．should take
以下哪根线是关到位信号线（）。
A.900
B.901
C.902
D.903
