Book Description
This Official Guide from GMAC outshines all others, simply because the questions are chosen from actual past tests and are very thoroughly researched. Equally important the answer choices for each question are also well thought out and both the correct and the incorrect choices reflect actual test patterns. (All other guides fail in this essential regard; even if their questions and the correct answer are realistic, their incorrect answer choices are often far-fetched or muddled.) The explanations for the answers in the Official Guide are crystal clear and very insightful.
The rules of grammar on which the GMAT Sentence Correction questions are based are best outlined in this guide. The section on Arguments is simply outstanding. I had a lot of difficulty with the Verbal section until I read through the explanations here. I scored in the 99th percentile in both sections and owe my success mostly to this guide (and the Princeton Review guide to a lesser extent.)
The absolute best part of the guide is that it not only explains clearly why an answer choice is correct, but also explains why the other choices are wrong. This is most useful since it shows you the patterns and tricks used on the actual test to lead you astray from the correct answer. Once you see the patterns, you can quickly identify and rule out the incorrect answers and pick out the best choice.
Buy this book
The Official Guide for GMAT Review, 10th Edition
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Related book
Verbal Workout for the GMAT, 2nd Edition (Graduate Test Prep)