求sin4分之3π解答过程程

来源：蜘蛛抓取(WebSpider) 时间：2017-02-04 14:35 标签： 阅读下面的解答过程
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求解答过程：阅读理解.
&&&& When skateboarding started in the 1960s, skateboards were made of wood and had clay wheels. Since the wheels did not grip concrete well, riders could do very few tricks with them. Soon people lost interest
in the sport.
&&&& In 1973, though, a new wheel was invented in California. It was made of a plastic called urethane (氨基 甲酸酯). A skateboard with these wheels moved very quickly and it also gripped the concrete well. During
the next few years skateboards were further improved. The urethane was perfected, and because the boards
were shaped better, riders liked them better. These skateboards gave new life to skateboarding. && &The streets were not safe for skateboarding, although it was easy to ride on the streets. As a result,
skateboard parks sprang up. The first parks appeared in California and Florida. At first there were only outdoor parks that had concrete slopes with small curves (曲线). Then more exciting parks appeared which had steep downward slopes, banked curves, and vertical walls. Today, there are both indoor and outdoor parks. &&& &In most of these parks riders must wear helmets (头盔) as well as knee and elbow pads (护肘). This gear can prevent a fall from causing serious injury.
&&&& Whenever they ride, people should always use this safety equipment, and they should learn how to fall
safely. Many accidents happen during the first week of riding, so it is very important that riders be taught well.
1. Why were the new skateboards more popular?
A. They were safer than the older ones.
B. The older models were expensive.
C. They were stronger than the older ones.
D. People could do more tricks with them.
2. The underlined word "grip" in the first paragraph means "_____".
A. move over a surface without slipping
B. stick to
C. replace
D. break down
3. Skateboard parks developed because _____.
A. parents decided it would be a good idea
B. too many accidents happened on the streets
C. many streets did not allow skateboarding
D. most city parks did not allow skateboarding
4. Which of the following statements about skateboard parks is TRUE?
A. The first parks appeared in Scotland and Florida.
B. The earlier parks had steep slopes.
C. In the parks people don't have to wear helmets.
D. At first there weren't any indoor parks.
阿姨有爱90WN靓
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求解答过程：阅读下列材料,回答问
阅读下列材料,回答问题：
材料一 唐朝对外交通路线图
材料二 市舶之利最厚,若措置得宜,所得动以百万计.&
——宋高宗&&&
（1）结合唐朝对外交通路线图,写出三个与唐朝密切交往的国家.
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
（2）材料二反映出南宋经济的发展出现了什么新特点?结合所学知识分析这一特点的出现是哪些因素为其奠定了基础?
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
（3）结合两则材料,分析唐朝和南宋对外贸易的商路各具有什么特点?试从经济重心、科技发展方面说明商路变化的原因.
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&
（1）日本、新罗、天竺.（2）宋代海外贸易兴盛,政府鼓励海外贸易,并设立市舶司加以管理；关系：农业、手工业、商业的发展为海外贸易业的发展奠定了基础.（3）唐代陆路、海路并举；宋代以海路为主.原因：①经济重心：唐朝时南北经济发展较为平衡,南宋经济重心转移到南方.②科技发展：造船技术的提高,指南针应用于航海.
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