单选题 Daylight saving time (DST) is the convention of advancing clocks so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modem DST was first proposed in 1907 by William Willett. Many countries have used it since then; details vary by location and change occasionally.
General agreement about the day"s layout confers so many advantages that a standard DST schedule usually outranks efforts to get up earlier, even for people who personally dislike the DST schedule. The practice is mixed blessing, however.
For instance, retailers, sporting goods makers, and other businesses benefit from extra afternoon sunlight, as it induces customers to shop and to participate in outdoor afternoon sports. As the 1984 Fortune magazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven stores, and the National Golf Foundation estimated the extension would increase golf industry revenues $200 million to $300 million. Conversely, DST can adversely affect farmers and others whose hours are set by the sun, For example, grain harvesting is best done after dew evaporates, so when field hands arrive and leave earlier in summer their labor is less valuable. DST also hurts prime-time broadcast ratings and drive-in and other theaters.
Clock shifts correlate with decreased economic efficiency. In 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on U.S. stock exchanges. Clock shifts and DST rule changes have a direct economic cost, since they entail extra work to support remote meetings, computer applications and the like. For example, a 2007 North American rule change cost an estimated $500 million to $1 billion.
Extra afternoon daylight is said to reduce traffic fatalities. In 1975 the U.S. DOT conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction to be 1.5% to 2%, but the 1976 NBS review of the DOT study found no differences in traffic fatalities. In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians. Others have found similar reductions. Single/Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST. A correlation between clock shifts and accidents has been observed in North America but not in Sweden. If this effect exists, it is far smaller than the overall reduction in fatalities.
However, the effect of DST on crime is less clear. In the 1970s the U.S. Law Enforcement Assistance Administration (LEAA) found a reduction of 10% to 13% in Washington, D.C."s violent crime rate during DST. However, the LEAA did not filter out other factors, and it examined only two cities and found crime reductions only in one and only in some crime categories; the DOT decided it was "impossible to conclude with any confidence that comparable benefits would be found nationwide". Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.
DST also has mixed effects on health. In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise. It alters sunlight exposure; whether this is beneficial depends on one"s location and daily schedule, as sunlight triggers vitamin D synthesis in the skin, but overexposure can lead to skin cancer. Sunlight strongly influences seasonal affective disorder. DST may help in depression by causing individuals to rise earlier, but some argue the reverse. The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for U.S. DST extensions, but DST can hurt night blindness sufferers.
Clock shifts disrupt sleep and reduce its efficiency. Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks. The government of Kazakhstan cited health complications due to clock shifts as a reason for abolishing DST in 2005.
Although the DST increases opportunities for outdoor leisure activities during afternoon sunlight hours, obviously it does not change the length of the day; the longer days nearer the summer solstice in high latitudes merely offer more room to shift apparent daylight from morning to evening. And the DST is commonly not observed during most of winter, because its mornings are darker: workers may have no sunlit leisure time, and children may need to leave for school in the dark.

单选题 According to the passage, the DST

单选题 Which of the following businesses may NOT benefit from the DST?

单选题 What is the role of the third paragraph in the development of the topic?

单选题 According to the effects of DST on various aspects, we can conclude that

单选题 What kind of writing does the passage belong to?