There (1) not one type of reading but several according to your reasons for reading. To read efficiently, 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 to6k 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) to 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. 9（）

A. which
B. that
C. at which
D. at that