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请根据短文的内容,回答题。 Maglev Trains (1) A few countries are using powerful electromagnets to develop high-speed trains, calledmaglev trains. Maglev is short for magnetic levitation, which means that these trains float over a guide way using the basic principles of magnets to replace the old steel wheel and track trains. (2) If you&39;ve ever played with magnets, you know that opposite poles attract and like poles repel each other. This is the basic principle behind electromagnetic propulsion. Electromagnets are similar to other magnets in that they attract metal objects, but the magnetic pull is temporary. You can easily create a small electromagnet yourself by connecting the ends of a copper wire to the positive and negative ends of an AA-cell battery. This creates a small magnetic field. If you disconnect either end of the wire from the battery, the magnetic field is taken away. (3) The magnetic field created in this wire-and-battery experiment is the simple idea behind a maglev train rail system. There are three components to this system: A large electrical power source, metal coils lining a guide way or track, and large guidance magnets attached to the underside of the train. (4) The big difference between a maglev train and a conventional train is that maglev trains do not have an engine -- at least not the kind of engine used to pull typical train cars along steel tracks4. The engine for maglev trains is rather unnoticeable. Instead of using fossil fuels, the magnetic field created by the electrified coils in the guideway walls and the track combines to propel the trains. (5) The magnetized coil running along the track, called a guideway, repels the large magnets on the train&39;s undercarriage, allowing the train to levitate between 1 to 10 cm above the guideway. Once the train is levitated, power is supplied to the coils within the guideway walls to create a unique system of magnetic fields that pull and push the train along the guideway. The electric current supplied to the coils in the guideway walls is constantly alternating to change the polarity of the magnetized coils. This change in polarity causes the magnetic field in front of the train to pull the vehicle forward, while the magnetic field behind the train adds more forward thrust. (6) Maglev trains float on a cushion of air, eliminating friction. This lack of friction allows these trains to reach unprecedented ground transportation speeds of more than 500 kph, or twice as fast as the fastest conventional train. At 500 kph, you could travel from Paris to Rome in just over two hour$amp; Paragraph 3 __________ 查看材料
A.
The main components of the maglev train system
B.
High-speed maglev due to zero friction
C.
The working principle of the maglev train
D.
Differences between polarity and magnetic field
E.
Comparison of maglev trains with traditional ones
F.
Maglev with a powerful motor
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【简答题】共同基金是人们在自愿的基础上,以一定的方式组织基金,并在金融市场上进行投资,以获取较高收益的金融组织,它可分为( )共同基金和( )共同基金两种。
【单选题】人们在自愿的基础上,以一定的方式组织基金,并在金融市场上进行投资,以获取高收益的金融机构是( )。
A.
保险公司
B.
信托公司
C.
共同基金
D.
证券公司
【简答题】若有定义 double a,*p=&a;则利用指针p和scanf函数给变量a输入数据的赋值语句是【1】.
【简答题】若有定义 double a,*p=&a; 则通过指针p和scanf函数给变量a输入数据的赋值语句是【 】.
【简答题】若有定义 double a,*p=&a; 则通过指针p和scanf函数给变量a输入数据的赋值语句是【1】.
【单选题】若有定义double *p;,且成功执行了语句:p=(double*)malloc(120);,则下面说法正确的是
A.
)可以将一个长度小于120的字符串拷贝到p所指空间
B.
可以将p用作含有30个float型元素的数组
C.
可以将p用作含有15个double型元素的数组
D.
p所指空间为默认的int型数组,且有30个int型元素
【单选题】人们在自愿的基础上,以一定的方式组织基金,并在金融市场上进行投资,以获取收益的金融机构是( )。
A.
保险公司
B.
信托公司
C.
共同基金
D.
证券公司
【简答题】是人们在自愿的基础上,以一定的方式组织资金,并在金融市场上进行投资,以获取高收益的金融组织。
【单选题】人们在自愿的基础上,以一定的方式组织基金,并在金融市场上进行投资,以获取高收益的金融机构是( )。
A.
保险公司
B.
共同基金
C.
信托公司
D.
证券公司
【单选题】进行分类汇总操作前,先对分类字段进行()操作。
A.
排序
B.
筛选
C.
高级筛选
D.
升序排序
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