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【单选题】
The Pony Express In the United States today, we can send a letter from coast to coast in just a few days for well under half dollar. But news did not always travel as fast or as cheaply as it does today. In the mid 180Os, trains and horse-drawn coaches carried mail. It took many weeks for news to travel from New York to California. In 1860, the railroad and telegraph reached only from the East Coast to Missouri, less than halfway across the country. Horse-drawn coaches, which were very slow, then carried the mall from Missouri to California. In April 1860, the Pony Express began to carry the mail from St. Joseph, Missouri, to Sacramento, California. The trip took just ten days——half the time the coaches took. The Pony Express was a home relay system. There were stations every 10 or 15 miles along the route, which was nearly 3,200 kilometers (2,000 miles) long. Fresh homes were at each station. The riders, with their heavy mailbags, changed homes at every station. They continued riding full speed for a total of about 100 miles. Then another rider took over and continued riding. The Pony Express riders rode through dangerous territory, including mountains., deserts, and Indian lands. Bad weather didn't stop these tough riders, either. They rode through rain, snow, sleet, and blizzards, both night and day. The riders, therefore, had to be both brave and strong. Some newspapers in 1860 carried this advertisement: Wanted: Young, skinny, wiry fellows, not over 18. Must be expert riders, willing to risk death daily. Orphans preferred. Most of the young Pony Express riders completed the ride successfully. Some of them even became famous for their courage and bravery during difficult rides. What did these young men get paid for their bravery? Twenty-five dollars a week. And what was the cost of sending a letter by Pony Express? Five dollars a half-ounce in 1860, then reduced to two dollars in 1861. In October 1861, the telegraph reached California. The Pony Express disappeared after this and became a short but exciting chapter in American history. What is the usage of the Pony Express?
A.
To help people travel from coast to coast.
B.
To train ridem for competition.
C.
To transfer materials and messages.
D.
To arrest criminals in the West.
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【简答题】以下有关 DF 检验的说法正确的有 ( ) 。 A . DF 检验的零假设是“被检验时间序列平稳” ; B . DF 检验的零假设是“被检验时间序列非平稳” ; C . DF 检验是单侧检验 ; D . DF 检验是双侧检验 ; E . DF 检验包含序列差分的滞后项 。A.B.C.D.E. E
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【单选题】在我国,储蓄存款都能获得利息。存款利息的多少取决于() ①收入水平 ②物价水平 ③利息率水平 ④本金、存期
A.
①②
B.
③④
C.
①③
D.
②④
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A.
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B.
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C.
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D.
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A.
正确
B.
错误
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A.
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B.
DF检验要求序列必须为AR(1)过程
C.
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D.
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