There are three main types of skimming,as suggested by Mc Whorter(1987).the first type is preview skimming. The aim of previewing is to attain a quick impression of a text. This helps the reader to decide whether the text is worth more careful reading.If the reader is familiar with the subject matter, he may only need to run his eyes down the page.A common
method of this type of reading is to read the first and last sentences of the first and last paragraph,and the first lines of the other paragraphs.