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问题 单项选择题

下列何种处理方式不影响CT图像噪声的改变（）

A.改变电流量

B.改变扫描范围

C.改变准直

D.改变球管到探测器的距离

E.改变矩阵

答案

参考答案：B

解析：噪声是指采样过程中接收到的一些干扰正常信号的信息，信噪比也会因此降低，主要影响图像的密度分辨力，使图像模糊失真。

单项选择题

Passage One


It is quite reasonable to blame traffic jams, the cost of" gas and the great speed of modern life, but manners on the toad are becoming horrible. Eye,body knows that the nicest men would become fierce tigers behind the wheel. It is all right to have a tiger in a cage, but to have one in the driver’s seat is another matter.
Road politeness is not only good manners, but good sense too. It takes the most cool-headed drivers great patience to give up the desire to beat back when forced to face rude driving. On the other hand, a little politeness goes a long way towards reducing the possibility of quarrelling and fighting. A friendly nod or a wave of thanks in answer to an act of politeness helps to create an atmosphere of good will and calmness so necessary in modern traffic conditions. But such behaviors of politeness are by no means enough. Many drivers nowadays don’t even seem able to recognize politeness when they see it.
However, misplaced politeness can also be dangerous. Typical examples are the driver who waves a child crossing the street at a wrong place into the path of oncoming cars that may be not able to stop in time. The same goes for encouraging old ladies to cross the road wherever and whenever they want to.
An experienced driver, whose manners are faultless, told me it would help if drivers learnt to correctly join in traffic stream without causing total blockages that give rise to unpleasant feelings. Unfortunately, modern drivers can’t even learn to drive,let alone master the roadmanship. Years ago, experts warned us that the fast increase of the car ownership would demand more give-and-take from all road users. It is high time for all of us to take this message to heart.

Troubles on the road are often caused by______.

A．traffic jams

B．the behavior of the drivers

C．great speed

D．terrible road conditions
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单项选择题

唯物辩证法的实质与核心是（）。

A.对立统一规律

B.量变质变规律

C.否定之否定规律

D.物质不灭定律
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