The first Starbucks coffee shop opened in 1971 in downtown Seattle, Washington, in the United States. It was a small coffee shop that roasted its own coffee beans. The coffee shop’s business did well, and by 1981 there were three more Starbucks stores in Seattle.
   Things really began to change for the company in 1981. That year, Howard Schultz met the three men who ran(经营) Starbucks. Schultz worked in New York for a company that made kitchen equipment. He noticed that Starbucks ordered a large number of special coffee makers, and he was curious about the company. Schultz went to Seattle to see what Starbucks did, and he liked what he saw. He wanted to become part of the company. In 1982, the original(原先的) Starbucks owners hired Schultz as the company’s head of marketing.
   In 1983, Schultz travelled to Italy. The unique atmosphere of the coffee bars there caught his eye. To Schultz it seemed that Italians spent their daily lives in three places: home, work and coffee bars. His experience in Italy gave Schultz a new idea for Starbucks back in Seattle.
Schultz created an atmosphere for Starbucks coffee shops that was comfortable, and customers everywhere seemed to like it. Between 1987 and 1992, Starbucks opened 150 new stores—and that was only the beginning. In fact, by the year 2000, three new Starbucks stores opened somewhere around the world every day!
   Today, Starbucks has thousands of stores, including stores in twenty-six countries. One thing that helps make Starbucks succeed in cities outside the United States is the way Starbucks works with local stores and restaurants. By working together with a store already in the city, Starbucks gets an understanding of customers in the city. This understanding helps Starbucks open stores in the right locations for their customers.

2015年，“中国游客”在全球范围内成为一个热门话题。中国旅游研究院数据显示，中国大陆出境游人数和购买力已连续3年居世界第一；2015年，中国大陆公民出境游人次实现16%的增长，首次突破1．2亿。这（    ）

①有利于增强我国出口创汇能力

②标志着对外开放进入了一个新阶段

③反映出我国居民收入得到提高

④会推动我国相关服务业的发展和进步

若对任意$x\in A,y\in B,\left(A,B\subseteq R\right)$有唯一确定的$f\left(x,y\right)$与之对应，称$f\left(x,y\right)$为关于$x$、$y$的二元函数.现定义满足下列性质的二元函数$f\left(x,y\right)$为关于实数$x$、$y$的广义“距离”:
（1）非负性:$f\left(x,y\right)\ge 0$，当且仅当$x=y=0$时取等号；
（2）对称性:$f\left(x,y\right)=f\left(y,x\right)$；
（3）三角形不等式:$f\left(x,y\right)\le f\left(x,z\right)+f\left(z,y\right)$对任意的实数z均成立.
今给出四个二元函数:①$f\left(x,y\right)=x^2+y^2$；②$f\left(x,y\right)={\left(x-y\right)}^2$；③$f\left(x,y\right)=\sqrt{x-y}$；④$f\left(x,y\right)=\sin \left(x-y\right)$.

能够成为关于的$x$、$y$的广义“距离”的函数的所有序号是（     ）

2017年1月9日，国务院将国家最高科学技术奖授予赵忠贤院士与屠呦呦研究员两位科学家．我国科学家屠呦呦因发现用于治疗疟疾的药物﹣﹣青蒿素 （化学式为C₁₅H₂₂O₅），因而获得2015年诺贝尔生理学及医学奖．下列关于青蒿素的叙述错误的是（   ）