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问题 单项选择题

对一路信号进行频移键控(FSK)调制时，若载波频率为fc,调制后的信号频率分别为 f1和f2(f1＜f2)，则三者的关系是 (1) 。当对多路信号进行调制时，调制后各信号的频谱

(2) 。信号到达接收端后通过 (3) 分离各路信号。WDM与FDM工作方式很相似，但WDM调制的是 (4) 。ILD是 (5) 使用的设备。

1（）

A．fc-f1＝f2-fc

B．f1*f2＝fc

C．f2+f1＝fc

D．f2-f1＝fc

答案

参考答案：A

单项选择题

If you left your book on the table overnight, you would find the following morning that it was still exactly when you had left it, provided nobody had moved it. If a ball is made to roll on a very smooth surface, it will roll a long distance unless something stops it or changes its direction. This tendency of an object to remain at rest unless something moves it and to continue moving unless something stops it is known as the Law of Inertia.
The following examples show the truth of this law.

  • (a) Put a table-cloth on a table and arrange a pile of books on it. Hold one edge of the tablecloth and pull it quickly. The table-cloth will come off, leaving the pile of books undisturbed.
  • (b) Place a small piece of cardboard on an open jar and place a coin on it directly over its mouth. Use one finger to flick the piece of cardboard away. You will notice that the coin drops into the jar.
  • (c) Sitting in a car which starts suddenly, you feel you are jerked backwards. In fact, you are not jerked backwards. Your lower half, which is in contact with the cushion, is forced to move forward with the car, and the upper part of your body, which remained at rest, is left behind.


Which of the following is an example of inertia

A．A boat can stay on water.

B．A plane can fly in the air.

C．You can walk faster on a very smooth surface.

D．You can go forward and backward on a swin
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多项选择题

全电子点火系统的组成（）

A、各种传感器

B、电子控制器（ECU）

C、点火电子组件

D、点火线圈

E、断电器

F、火花塞
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