A、To know direction. B、To measure time. C、To show off one’s wealth. D、To get to work on time. C短文提到，进入19世纪后，戴手表的一个主要目的是向别人炫耀自己的财

Watches and clocks seem as much a part of our life as breathing or eating. And yet, did you know that watches and clocks were scarce in the United States until the 1850s?
    In the late 1700s, people didn’t know the exact time unless they were near a clock. Those delightful clocks in the squares of European towns were built for the public-after all, most citizens simply couldn’t afford a personal timepiece. Well into the 1800s—in Europe and the United States—[17]the main purpose of a watch, which, by the way, was often on a gold chain, was to show others how wealthy you were.
    The word "wristwatch" didn’t even enter the English language until nearly 1900. By then the rapid pace of industrialization in the Unites States meant that measuring time had become essential. How could the factory worker get to work on time unless he or she knew exactly what time it was?[18]Since efficiency was now measured by how fast a job was done, everyone was interested in time. And since industrialization made possible the manufacture of large quantities of goods, watches became fairly inexpensive. Furthermore, electric lights kept factories going around the clock. Being on time had entered the language —and life—of every citizen.
16. When did watches and clocks become common in the United States?
17. What was the main purpose of having a watch during the 1800s?
18. Why was everyone interested in time by 1900?