Example：

　　Whether the world is Euclidean or non-Euclidean is still an open question.

　　However， if a star's position is predicted based on non-Euclidean geometry，

　　then when a telescope is pointed toswheresthe star should be it will be ther

　　e. Whereas， if the star's position is predicted based on Euclidean geometry，

　　then when a telescope is pointed toswheresthe star should be it won't be th

　　ere. This strongly indicates that the world is non-Euclidean.

　　Which one of the following best expresses the main idea of the passage？

　　（A） The world may or may not be Euclidean.

　　（B） The world is probably non-Euclidean.

　　（C） The world is non-Euclidean.

　　（D） The world is Euclidean.

　　（E） The world is neither Euclidean nor non-Euclidean.

　　Choice （A） understates the main idea. Although the opening to the passage st

　　ates that we don't know whether the world is non-Euclidean， the author goes

　　on to give evidence that it is non-Euclidean. Choice （C） overstates the main

　　idea. The author doesn't say that the world is non-Euclidean， just that evi

　　dence strongly indicates that it is. In choice （B）， the word “probably” prop

　　erly limits the scope of the main idea， namely， that the world is probably n

　　on-Euclidean， but we can't yet state so definitively. The answer is （B）。

　　Premises

　　Once you've found the conclusion， most often everything else in the argument

　　will be either premises or “noise.” The premises provide evidence for the c

　　onclusion； they form the foundation or infrastructure upon which the conclus

　　ion depends. To determine whether a statement is a premise， ask yourself whe

　　ther it supports the conclusion. If so， it's a premise. Earlier we saw that

　　writers use certain words to flag conclusions； likewise writers use certain

　　words to flag premises. Following is a partial list of the most common premi

　　se indicators：