问题 选择题

反证法证明“三角形中至少有一个角不小于60°”先应假设这个三角形中(  )

A.有一个内角小于60°

B.每个内角都小于60°

C.有一个内角大于60°

D.每个内角都大于60°

答案

设三角形的三个角分别为:a,b,c.

假设,a<60°,b<60°,c<60°,

则a+b+c<60°+60°+60°,

即,a+b+c<180°与三角形内角和定理a+b+c=180°矛盾.

所以假设不成立,即三角形中至少有一个角不小于60°.

故选B.

单项选择题
单项选择题

"The impulse to excess among young Britons remains as powerful as ever, but the force that used to keep the impulse in check has all but disappeared," claimed a newspaper. Legislation that made it easier to get hold of a drink was "an Act for the increase of drunkenness and immorality", asserted a politician.

The first statement comes from 2005, the second from 1830. On both occasions, the object of scorn was a parliamentary bill that promised to sweep away " antiquated" licensing laws. As liberal regulations came into force this week, Britons on both sides of the debate unwittingly followed a 19th-century script.

Reformers then, as now, took a benign view of human nature. Make booze cheaper and more readily available, said the liberalisers, and drinkers would develop sensible, continental European-style ways. Nonsense, retorted the critics. Habits are hard to change; if Britons can drink easily, they will drink more.

Worryingly for modern advocates of liberalisation, earlier doomsayers turned out to be right. Between 1820 and 1840, consumption of malt (which is used to make beer) increased by more than 50%. Worse, Britons developed a keener taste for what Thomas Carlyle called "liquid madness"—gin and other spirits.

The backlash was fierce. Critics pointed to widespread debauchery in the more disreputable sections of the working class. They were particularly worried about the people who, in a later age, came to be known as "ladettes". An acute fear, says Virginia Berridge, who studies temperance at the London School of Hygiene and Tropical Medicine, was that women would pass on their sinful ways to their children.

In the 19th century, temperance organisations set up their own newspapers to educate the public about the consequences of excess. That, at least, has changed: these days, the mainstream media rail against the demon drink all by themselves.

Which of the following could be the best title for the text()

A. Old Wine, New Bottle

B. Mainstream Media, Nonsense

C. Doomsayers, Unwarranted Arguments

D. Fierce Backlash, Immorality