Understanding GMAT-specific grammar is crucial to increasing your Sentence Correction score. 

What is GMAT grammar? It's whatever the writers of the test want it to be. 

There is always an objective reason that one answer choice is "more correct" than the others. Learning to identify WHY these sentences are preferable is the problem. You're certainly not going to find the explanations in the Official Guide (e.g. "this sentence is awkward."). 

In this set of videos, Rowan Hand, author of the #1 Amazon Bestseller (GMAT and Test Preparation), Last Minute GMAT Grammar, breaks down necessary GMAT-specific grammar concepts in clear, easy language.

Never again will you have to worry about picking the sentence that "sounds correct" but isn't precise enough, or the sentence that "sounds wrong" but is correct for some reason.

Designed for both native and non-native English speakers, Complete GMAT Grammar Basics Part I provides as close to a comprehensive review of the nuanced, GMAT-specific grammar concepts as possible.

Check out Part I for Fundamental GMAT Grammar Topics!