在打开的SF6电气设备上工作的人员，应配置和使用必要的（）用具。
A、专用
B、绝缘
C、耐腐蚀
D、安全防护
参考答案：D
红斑作用
One-fifth of the light switches produced by a certain factory are defective. Four-fifths of the defective switches are rejected and of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective ？（）
A.4%
B.5%
C.6.25%
D.11%
E.16%
of the nondefective switches are rejected by mistake. If all the switches not rejected are sold, what percent of the switches sold by the factory are defective ？（）