Barbed wire, first patented in the United States in 1867, played an important part in the development of American farming, as it enabled the settlers to make effective fencing to enclose their land and keep cattle away from their crops. This had a considerable effect on the cattle ranching, since the herds no longer had unrestricted use of the plains for grazing, and the fencing led to conflict between the farmers and the cattle ranchers.
Before barbed wire came into general use, fencing was often made from serrated(边沿呈锯齿型的) wire, which was unsatisfactory because it broke easily when under strain, and could snap in cold weather due to contraction. The first practical machine for producing barbed wire was invented in 1874 by an Illinois farmer, and between then and the end of the century about 400 types of barbed wire were devised, of which only about a dozen were ever put to practical use.
Modern barbed wire is made from the mild steel, high-tensile steel, or alum
A. prevent the reel from advancing to rapidly
B. twist the wire
C. separate doublestranded wire
D. cut the wire that becomes barbs
Passage Four
When an icon (偶像) lasts for more than a century, there is a reason. But what is it about the teddy bear that makes it a lasting symbol in our society Trends experts say that when an icon is rooted in reality, when people grow to love it, and when it represents something larger, it tends to last.
America’s affair with the teddy bear began in the fall of 1902 when then-President Theodore Roosevelt went on a bear hunting trip in the South. He had no luck till the fifth day when he spotted a bear and raised his rifle to shoot--then lowered it when he saw a baby bear in the line of fire, eating honey from its paws. Roosevelt is reputed to have said, "I don’t shoot baby bears." Another story has Roosevelt refusing to shoot a wounded bear.
Washington Post cartoonist Clifford Berryman depicted the bear incidents and began using bears in many political cartoons on many subjects. Soon toy and novelty makers started creating
A. Eliminating inequality among people of different background.
B. Providing a cozy home to those who long for it.
C. Taking people's mind temporarily off the danger and meanness of the modem world.
D. Helping people better express themselves in writing greeting cards.
在一个16 000 m2建 筑面积的八层楼里，没有任何现成网线，现有1200台计算机需要连网，对网络的响应速度要求较高，同时要求WLAN覆盖整栋楼满足临时连网的需要。设计师 在进行物理网络设计时，提出了如下方案：设计一个中心机房，将所有的交换机、路由器、服务器放置在该中心机房，用UPS保证供电，用超5类双绞线电缆作为 传输介质，在每层楼放置一个无线AP。该设计方案的致命问题之一是（30) ，其他严重问题及建议是（31)。
空白处（30）应选择（）我来回答:
