问题 多项选择题

以下关于变压器的表述中,正确的有()。

A.电力变压器的铁损和铜损都很小,在满负荷运行时效率均在95%以上

B.三相电力变压器

C.变压器空载时效率为零

D.S11系列变压器的空载损耗比S9系列低25%

E.国家规定,当变压器安装地点的海拔不超过1000m时,绕组温升限值为65℃,上层油面温升的限值为55℃

答案

参考答案:A, B, C, E

解析:

S11系列变压器的空载损耗比S9系列低20%,S13系列变压器的空载损耗比S11系列低25%。

单项选择题
单项选择题

There (1) not one type of reading but several according to your reasons for reading. To read carefully, you have to (2) your reading speed and technique (3) your aim (4) reading. Skimming is a technique necessary for quick and efficient reading.

When skimming, you (5) the reading (6) quickly in order to get the (7) of it, to know how it is organized, (8) an idea of the tone or the intention of the writer. Skimming is (9) an activity which (10) an overall view of the text and (11) a definite reading competence.

Skimming doesn’t need reading all the material, but it doesn’t mean that it is an (12) skill for the lazy, because it need a high degree of alertness and concentration.

When you read, you usually start with (13) understanding and move towards detailed understanding rather than working the other way round. But (14) is also used after you have already carefully studied and you need to (15) the major ideas and concepts.

In order to be able to skim quickly and (16) through a text, you should know where to look for what you want. In preview skimming you read the introductory information, the headings and subheadings, and the summary, if one is provided. (17) this skimming, decide whether to read the material more thoroughly, and select the appropriate speed (18) you read.

The same procedure (19) for preview skimming could also be used to get an overview. Another method would be to read only key words. This is done by omitting the unnecessary words, phrases, and sentences.

In order to skim efficiently and fulfill your purpose, (20) practice is necessary.

4().

A.on

B.while

C.as

D.at