手持式用电设备及移动设备,不应安装漏电保护器作为末级保护。第五章P82
参考答案:错
My sister met him at the Grand Theatre yesterday aftemoon , so he _____ your lecture. [ ]
A. couldn't have attended
B. needn't have attended
C. mustn't have attended
D. shouldn't have attended
简述根管治疗的适应证。