问题 单项选择题

An analog signal’s characteristic quantity representing data may (66) . at any instant, any value within a continuous (67) . For example, an analog signal may follow continuously the values of another physical quantity representing data.

A discrete signal is composed of (68) elements in time, each element having one or more characteristic quantities which can represent data. Examples of characteristic quantities are amplitude, waveform, (69) , and position in time. A digital signal is a special case of discrete signals, in which data are represented by a (70) number of well-defined discrete values that one of its characteristic quantities may take in time.

(70)处填()。

A.limited

B.finite

C.restricted

D.bounded

答案

参考答案:B

解析:

[参考译文]

模拟信号表示数据的特征量,在任一时刻,可取某一连续区间内的任一值。例如,模拟信号可以连续地跟随表示数据的另一物理量的值。

离散信号由时间上相继的各元素组成,其中每一元素都有一个或多个能表示数据的特征量。特征量的例子有振幅、波形、持续时间和当时位置。数字信号是离散信号的一种特例,其中的数据由已明确定义、个数有限的离散值来表示,各值均可由该信号的特征量之一随时间来取。

完形填空
信息归纳 (本部分共5小题,每小题1分,共5分)
Scientists who study the climate (气候) are still arguing about how fast the earth is warming and how much it will warm, but they do agree that the earth is warming and that it will keep warming if we don’t do anything about it.
Scientists agree that the burning of fossil fuels (化石燃料) like oil and coal cause greenhouse gases to escape (释放) into the air and that these gases are causing most of the warming. Another cause is deforestation ( cutting down trees ) . Trees soak up carbon dioxide  (二氧化碳) , one of the greenhouse gases, from the air.
There are already some changes happening because of global warming. Sea level is rising and some animals are already moving to new homes. It’s already too late to stop global warming completely.
If the warming gets worse, as scientists expect, there may be some kinds of plants and animals that become extinct (灭绝的) because they can’t move to new homes. There may be more storms and floods. Sea level may rise so much that people have to move away from the coasts. Some areas may become too dry for farming.
Global warming is a very difficult problem to fix. People are having a hard time agreeing on what to do about it. For example, everyone agrees that wasting energy is a bad thing to do. But some people think that the federal government (联邦政府) should make laws about it, while other people think it should be up to each person or business to decide what to do.
Many states and businesses in the United States are not waiting until the federal government decides what to do. They have already started working on the problem.
根据短文内容,完成下面表格中的信息。每空词数不限。
Global warming
Causes
1. ______                 __  ;
2. _______                _  ; 
Possible results
3. _______                 _  .
Plants and animals become distinct.
4. _____             _   __  .
People move away from coasts.
Some areas become too dry for farming.
What to do
5. _______                _  .
 
单项选择题