本质安全型电器设备的电源有()。
A.直流电源
B.交流电流
C.独立电源
D.外接电源
参考答案:C, D
Many species of animals are in danger of ________ due to the pollution these days. [ ]
A. dying out
B. dying away
C. dying off
D. dying down
防腐剂苯甲酸的一般用量为()
A.0.01%~0.25%
B.0.2%~0.3%
C.1%~3%
D.2%
E.0.1%~0.25%