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  3. Barbed wire, first patented in the United States in 1867, played an important part in the development of American farming, as it

Barbed wire, first patented in the United States in 1867, played an important part in the development of American farming, as it

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问题     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 aluminum. Mild steel and aluminum barbed wire have two strands twisted together to form a cable which is stronger than single-strand wire, round or oval, is made from high-tensile steel with the barbs crimped(使弯曲) or welded on. The steel wires used are galvanized—coated with zinc(锌) to make them rustproof. The two wires that make up the line wire or cable are fed separately into a machine at one en& They leave it at the other end twisted together and barbed. The wire to make the barbs is fed into the machine from the sides and cut to length by knives that cut diagonally(对角线)through the wire to produce a sharp point. This process continues automatically, and the finished barbed wire is wound onto reels, usually made of wire, in lengths of 400 meters or in weights of up to 50 kilograms.
选项 A、Easier installation.
B、Improved rust-resistance.
C、Increased strength.
D、More rapid attachment of barbs.
答案C
解析 本题为细节辨认题。文章在第三段开头就指出现代的铁丝网的材料不同于过去，它由双股构成因而更为结实。
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