单项选择题

Passage Four 
Questions 16 to 20 are based on the following passage. 
   It is hard to imagine life without Arabic numbers(数字). No other number system ever invented has a simple way to write a number like 1984. In Roman numeral, it comes out like this MCMLXXXIV. Imagine how difficult it would be for a school pupil to remember it! 
   The Arabs, however, call their numbers “Indian numerals”. This is probably because they got the original idea a long time ago from India. There were no printed newspapers or scientific magazine then, so mathematics traveled along the same routes that silk did, as businessmen sold and bought goods. The Arabs took the new numbers and made improvements that quickly led to advances in technology. 
   The achievement of Arabic technology can be seen from a passage in a 10th-century book about an Arabic city:” The neighboring country showed the results of careful work in agriculture, trade, and industry. Rice and many other plants were grown in fields with water supplied by Arab engineers. The city included 900 public baths, stone-covered streets, fountains, and beautiful buildings.” At this time, London was a small town with dirty streets, and Berlin was a farming village. In fact, cities outside the Arab world did not reach the same level of social development until centuries later.

It takes much more efforts to（）

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