题目

 某研究性学习小组利用荧光素-荧光素酶生物发光法，测定人参愈伤组织中 ATP的含量，以研究人参细胞能量代谢的特点。 实验原理：荧光素在荧光素酶、ATP等物质参与下，进行反应发出荧光；用分光光度计可测定发光强度；当荧光素和荧光素酶都足量时，在一定范围内，ATP的含量与发光强度成正比。 实验步骤： 一、ATP的提取：称取一定量的人参愈伤组织，研磨后沸水浴10min，冷却至室温，离心，取上清液。 二、ATP的测定：吸取一定量的上清液，放 Everybody hates it，but everybody does it．A recent report said that 40％of Americans hate tipping．But why do tips exist? The common opinion in the past was that tips both rewarded the efforts of good service and reduced uncomfortable feelings of inequality．It is believed that the better the service is，the bigger the tip will be． But according to a new research from Cornell University，tips no longer serve any useful function．The paper analyzes number they got from 2，547 groups dining at 20 different restaurants．The connection between larger tips and better service was very weak． Tipping is better explained by culture than by the money people spend．In America，tipping is regarded as part of the accepted cost of a service．In New York restaurants，failing to tip at least 15％could well mean dissatisfaction from the customers Hairdressers can expect to get 15％一20％．and the mall who delivers your fast food should be paid$2．In Europe，tipping is less common．In many restaurants the amount of tip is decided by a standard service charge In many Asian countries，tipping has never really caught on at a11．Only a few have really taken to tipping。 According to Michael Lynn，the Cornell papers’author，countries in which people are more social or outgoing tend to tip more．tie says，“In America，where people are expressive and eager to mix up with others，tipping is about social approval If you tip badly，people think less of you .Tipping well is a chance to show off．”68．This passage is mainly about         A．different kinds of tipping in different countries B．the relationship between tipping and countries C．the origin and present meanings of tipping D．the reason why American people hate tipping69．Which of the following best explains the underlined phrase“caught on”in paragraph 4? A．been hated      B．become popular   C．been stopped    D．been permitted70．Eating in a well—known restaurant in New York，who is likely to tip most? A．A Frenchman．    B．A Chinese．  C．A Japanese．    D．An American．71．We can infer from this passage that        ． A．tipping is no longer a good way to satisfy some customers themselves B．tipping has something to do with people’s character C．tipping in America can make service better nowD．tipping is no longer popular in New York