题干

已知△ABC与△DEF是关于点P的位似图形,它们的对应点到P点的距离分别为3cm和4cm,则△ABC与△DEF的面积比为(  )

A:3:4

B:3:7

C:9:16

D:9:49

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答案(点此获取答案解析)

C

同类题1

阅读理解

    The online economy—from search to email to social media—is built in large part on the fact that consumers are willing to give away their data in exchange for products that are free and easy to use. The assumption behind this trade-off is that without giving up all that data, those products either couldn't be so good or would have to come at a cost.

    But a new working paper, released this week by Lesley Chiou of Occidental College and Catherine Tucker of MIT, suggests that the trade-off may not always be necessary. By studying the effects of privacy regulations in the EU, they attempted to measure whether the anonymization(匿名化) of search data hurts the quality of search results.

    Most search engines capture user data, including IP addresses and other data that can identify a user across multiple visits. This data allows them search companies to improve their algorithms(算法) and to personalize results for the user. At least, that's the idea. To determine whether storage of users' personal data improves search results, Chiou and Tucker looked at how search results from Bring and Yahoo differed before and after changes in the European Commission's rules on data retention(数据保存). In 2008 the Commission recommended that search engines reduce the period over which search engines kept user records. In response, Yahoo decided to strengthen its privacy policy by anonymizing user data after 90 days. In 2010 Microsoft changed its policy, and began deleting IP addresses associated with searches on Bring after six months and all data points intended to identify a user across visits after 18 months. In 2011 Yahoo changed its policy again, this time deciding to store personal data longer—for 18 months rather than 90 days—allowing the researchers yet another chance to measure how changes in data storage affected search results.

    The researchers then looked at data from UK residents' web history before and after the changes. To measure search quality, they looked at the number of repeated searches, a signal of dissatisfaction with search results. In all three cases, they found no statistically significant effect on search result quality following changes in data retention policy. In other words, the decision to anonymize the data didn't appear to impair the search experience. “Our results suggest that the costs of privacy may be lower than currently perceived,” the authors write, though they note that previous studies have come to different conclusions.

同类题2

请先阅读下面短文,掌握其大意,然后从各小题所给的A 、B、C、D四个选项中选出可以填入相应空白处的最佳选项。

    Things like Hula hoops(呼啦圈)used to be very popular. Did you ever own any of these? If you didn't, don't feel too bad. They were all fads. A fad is something that becomes very 1 among a large number of people, but only for a short time.2 can become a fad very quickly, but can stop being popular just as quickly.3 it is no longer “cool,” a fad goes away. Anything can become a(n) 4-fashion, food, music, technology, even language.

    In the late 1970s, Erno Rubik, a professor was looking for a 5 way to teach his students about 3D objects. He 6 a six-color plastic object that would be called the Rubik's Cube(魔方). The goal was to get each side of the cube a 7 color. It was very challenging. It took a few years for the toy to become popular, but then 8, in 1982, it seemed everyone had one. People bought over a hundred million of the9. There were 50 books available that year offering solutions(解决办法). Then, just as suddenly as the craze (风尚) started, it 10. By 1983, people were not interested in the Rubik’s Cube anymore, perhaps because so many people 11 had one in their home.

    In 2012, a South Korean musician named Psy released a song called “ Gangnam (江南) Style.” The music video shows Psy pretending (假装) to horse-ride while he is dancing. In six months, it became the first Youtube (一视频网站) video ever to reach a billion views (观看). Six months after that,12 went on to reach two billion views. The song and video started a worldwide 13 craze. “Gangnam Style” had a huge influence on world popular culture. U.S. President Barack Obama and U.K. Prime Minister David Cameron even 14 the dance. “Gangnam Style” became less and less popular,15 the “Korean Wave” of culture remains popular all over the world.