应定期检查防雷装置的受雷导体及其构架有无锈蚀或机械损伤而发生断裂等情况。如发现锈蚀在

下列名称或化学式一定表示纯净物的是（　　）

A．氯乙烯

B．聚乙烯

C．C₃H₇Cl

D．(C₆H₁₀O₅) _n

关于冠脉循环的解剖特点下列叙述中错误的是（）

A．心肌的血液供应来自左、右冠状动脉

B．冠状动脉起源于主动脉根部

C．在多数人中，左冠状动脉主要供应左心室的后部和右心室

D．左冠状动脉的血液流经毛细血管和静脉后，主要经由冠状窦回流入右心房

E．右冠状动脉的血液则主要经较细的心前静脉直接回流入右心房

简述翻车机在空车时的安全工作重点？

When I was an editor, I always preferred to apologise promptly, what the merits of the case, rather than face the expense and, importantly, the time consuming complexities and debilitating worry of litigation, libel being one of the least satisfactory branches of the law.

A．whichever, more importantly

B．whatever, more important

C．whichever, more important

D．whatever, more importantly

比较下面两个化合物碱性大小：