信号把钩工在提升机运行期间必须精力集中,随时注视()罐门等运行的情况,发现异常及时采取措施。
A.指示信号
B.提升容器
C.连接装置
D.钢丝绳
参考答案:A, B, C, D
—Have you had your lunch ______?
—Yes, I have ______ had it.[ ]
A. already; yet
B. yet; already
C. yet; yet
写出下列物质的电子式:(每小题1分,共4分)
(1) 硫化氢: 氧气:
(2) 氯化铵: 过氧化钠: