题目

下列物质中，其物质的量为0.2mol的是A. 2.2g CO2 B. 4.8gMg C. 4.48L O2 D. 49g H2SO4 答案：【答案】B【解析】摩尔质量以g/mol为单位，数值上等于其相对分子质量或相对原子质量，根据n=来计算选项中各物质的物质的量，C选项中氧气所处状态不确定，气体摩尔体积不确定，不能计算其物质的量。A．CO2的摩尔质量为44 g/mol，2.2 g CO2的物质的量= = 0.05mol，不符合题意，故A项错误；B．Mg的摩尔质量MANY of us enjoy doing it: you turn on the camera on your mobile phone and hold it at a high angle (角度), making your eyes look bigger and your cheekbones more marked out. You turn to your best side and click. There it is – your selfie. Over the past year, “selfie” has become a well-known term across the globe. This August the Oxford dictionary added the word to their online dictionary and defined it as: “A photograph that one has taken of oneself, typically with a smartphone or webcam and uploaded to a social media website.” Today it’s not difficult to find social networking pages full of photos people have taken of themselves and their friends. And selfie culture has become especially related to young people. As many as 91 percent of teenagers have posted photos of themselves online, according to a recent survey by the US Pew Research Center. So what are the reasons for the rise of selfie culture? “The cult (狂热) of the selfie celebrates regular people,” Pamela Rutledge, a professor at the Massachusetts School of Professional Psychology, told Vogue magazine. “There are many more photographs available now of real people than models.” Posting selfies also allows you to control your image online. “I like having the power to choose how I look, even if I’m making a funny face,” Samantha Barks, 19, a high school student in the US, told Vogue. In addition to self-expression and documentation (记录), selfies “allow for an close friendship for long-distance friends, because you can see each other’s faces every day”, wrote Casey Miller at The Huffington Post. But US psychologist Jill Weber is concerned that selfies might lead to social problems. “There’s a danger that your self-esteem (自尊心) may start to be tied to the comments and ‘likes’ you get when you post a selfie, and they aren’t based on who you are – they’re based on what you look like,” Weber told Vogue. “When you get nothing or a negative response, your confidence can plummet.” 小题1:The first paragraph is intended to _________.A．explain why selfie is popularB．describe how to make selfieC．show the importance of selfieD．introduce the topic of selfie小题2:How many reasons for the rise of selfie culture are mentioned in the passage?A．TwoB．ThreeC．FourD．Five小题3:What is Jill Weber’s opinion about selfies?A．Comments on selfie are based on who you are.B．Selfies have more disadvantages than advantages.C．Others’ response to selfies might affect one’s self-esteem.D．Selfies shouldn’t be encouraged for they lead to social problems.小题4:The underlined word “plummet” in the last paragraph is closest in meaning to __________.A．go downB．calm downC．pick upD．build up