题干

人口的变化反映社会发展状况,从下表可推出的正确结论有(  )

朝代

南方

北方

人口(户)

占全国比例

人口(户)

占全国比例

西汉

2470685

19.8%

9985785

80.2%

唐朝

3920415

43.2%

5148529

56.8%

北宋

3025541

62.9%

1122476

37.1%

A:北方安土重迁的观念较淡薄

B:北宋的政治中心和经济重心均在南方,使南方人口大增

C:经济重心南移和战争频繁导致人口不断南迁

D:由北宋人口数量的减少可知汉唐经济远比宋代繁荣

上一题 下一题 0.0难度 选择题 更新时间:2019-12-11 10:39:08

答案(点此获取答案解析)

C

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阅读理解

    Who could have imagined that a treadmill(跑步机)on wheels would one day become a thing? Lopifit is an unusual means of transportation that allows you to power an electric bicycle by walking on a treadmill.

    Lopifit founder Bruin Bergmeester says it all started when he asked himself the question. "How can I use a treadmill outdoors?" He eventually came up with a design, to which he added an electric engine, and Lopifit was born. The treadmill bicycle is similar to a typical electric bicycle in that the motor only works when the rider puts power in as well. The Lopifit senses it when you walk on the treadmill and uses the motor to turn a drive chain at the back part of the treadmill, helping you reach a top speed of 17 miles per hour.

    To use the Lopifit, simply turn on the battery and use your feet to slide the treadmill backwards and activate (激活) the motor. Then get on and enjoy the ride! If you need speed, just walk on the treadmill, and if you want to coast, all you have to do is stay still and admire the view. To stop, you have two hand brakes available.

    The Lopifit first hit the streets in 2014 and, unsurprisingly, became an instant hit. That was actually quite challenging for the company, because it started get inquiries and calls for orders, but it was nowhere near ready for mass production. The unique treadmill bicycle became available this year, and Lopifit is struggling to keep up with demand, despite the high price tag of $ 2,115.

    But despite having a very loyal fan-base of so-called Lopifitters, the creative means of transportation also has naysayers who simply consider the invention stupid and unnecessary. They basically believe that if you're going to walk, you might as well do it the old-fashioned way. But the Lopifit does have the unique advantage of helping you walk really fast without breaking a sweat, or walking at cycling speed, if you will.