题干

下列命题中:

①两条对角线互相平分且相等的四边形是正方形;

②菱形的一条对角线平分一组对角;

③顺次连结四边形各边中点所得的四边形是平行四边形;

④两条对角线互相平分的四边形是矩形;

⑤平行四边形对角线相等.

真命题的个数是(   )

A:1

B:2

C:3

D:4

上一题 下一题 0.0难度 选择题 更新时间:2013-04-27 09:10:11

答案(点此获取答案解析)

B

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阅读理解

    Driving in Canada is similar to driving in many parts of the United States. Distances and speeds, however, are posted in kilometers per hour and some signs, particularly in Quebec, may only be in French.

    Unless otherwise posted, the maximum (最大限度的) speed limit in Canada is 50km/hr in cities and 80km/hr on highways. On rural highways, the posted speed limit may be 100km/hr. It is illegal to take automobile radar detectors (汽车雷达检测器) into Quebec, Ontario, Manitoba, and the Yukon. Seat belt use is required by law for all passengers, and child car seats must be used by children under 40 pounds. Some provinces require drivers to keep their vehicles' headlights on during the day and some have banned (禁止) driving while using a hand-held cell phone. Motorcycles cannot share a lane (车道), and safety helmets for motorcycle riders and passengers are necessary. Running a red light is a serious crime throughout Canada and drivers are advised to stop before starting when a light turns green.

    Winter travel can be dangerous due to heavy snowfalls and icy conditions. Some roads and bridges are often closed in winter. Snow tires are required in some provinces. Travelers should also be careful about animals while driving at night in rural areas.

    Highway 401, from Detroit to Montreal, is one of the busiest highways in North America. It has been the scene of many deadly traffic accidents due to sudden and severe weather changes, high rates of speed, and heavy truck traffic. Thus drivers should be alert while travelling here.

    Please refer to our Road Safety page for more information. Also, we suggest that you visit the website of Canada's national authority responsible for road safety.