单选题 A great deal of the early part of humanity's long struggle to measure time amounted to trying to decide what exactly it was that should be measured. The basic unit of time was the day — from sunrise to sunset. The Egyptians were the first to break the day into 12 equal parts, giving us the forerunner of today's hours. It was into that world of "natural time", based on the sun's march across the sky and varying with the seasons, that the first mechanical timepieces were introduced in 13th-century Europe. At odds with the conception of time as something that flows, with the introduction of the first clocks came the idea of measuring time by splitting it into discrete chunks and counting them. That the early clocks were highly unreliable was of little consequence because they could be checked and adjusted regularly by reference to the sun. So despite the technology, time still depended on the sun, and still varied from season to season. The "time" given by a mechanical device was not considered to be the real time and had to be indicated as such, by means of the phrase "of the clock", later abbreviated to "o'clock". Underlying the development of ever more accurate clocks came a new conception of time as something that flows of its own accord, in a uniform fashion, independent of the rotation of the earth or its motion around the sun. This view of time has become so ingrained that it is hard to step back and realize that time is a human invention, something that exists, in a practical sense, only by virtue of the machines we develop to "measure" it.(In fact, the thing we are measuring is created by the devices that do the measurement.) Another development in the ever-changing concept of time was brought about by the growth of the railways in the 19th century, particularly in North America. With reliable clocks, it was possible for people within towns to synchronise their daily activities. Rail travel necessitated coordination of all those different local times. The end result of this change is our system of time zones, with a uniform notion of time within each zone. After two thousand years, a completely abstract, human-made notion of time had been put in place. Human life would never be the same.

单选题 This text is mainly about ______.

单选题 Which one is true about people's idea about time before first clock appeared?

单选题 Which one of the following is true about the early clocks?

单选题 The origin of the word "o'clock" conveys the notion that______.

单选题 After more accurate clocks are invented, people form a new conception of time that_____.

单选题 The word "synchronise" in Paragraph 5 probably means ______.

单选题 The growth of the railways in the 19th century contributed to which of the following statements?