甲物质是一种重要的有机化工原料。一定质量的甲和48g乙按下图所示充分反应,当乙完全反应时,可生成44g丙和36g丁,则甲中所含各元素的质量比为
A.C:H=12:1 | B.C:H=3:1 | C.C:H:O=6:1:8 | D.C:H:O=3:1:4 |
--- Do you like watching TV?
---Yes, I. But only after I finish my homework.
A. | am | B. | do | C. | does | D. | did |
Li Yan is my best friend. She comes a small village.
A. | B. | C. | D. |
How is your father? Please say hello to ______ for me.
A. | she | B. | him | C. | it | D. | her |
下列关于实验室制氧气并用排水法收集的实验操作先后顺序中不正确的是()
A. | 先检查制氧装置的气密性,再装药品 |
B. | 先给试管均匀加热,再对着药品加热 |
C. | 等导管口排出的气泡均匀后,再将导管伸入盛水的集气瓶中 |
D. | 先熄灭酒精灯,再将导管从水槽中取出 |
某无毒气体的密度约是空气密度的5/9,且极难溶于水,那么收集该气体的方法可采用 ①向上排空气法②向下排空气法③排水法()
A. | ①② | B. | ①③ | C. | ②③ | D. | ①②③ |