The GMAT sentence correction section is about your ability to recognize the various elements of a GMAT sentence, elements such as 'dependent' and 'independenet clauses', qualifiers, subject and verb in the various clauses, and to make sure that the elements are logically, correctly, concisely, effectively, and correctly used to express an idea or a thought. Take a look at the following sentence: "1995 was the first year of sales increase".  What is wrong with this sentence?

Notice that the 'subject' of the sentence is '1995' whereas the 'logical subject' must be 'sales'. You will learn that the correct expression must read: "Sales first increased in 1995." Notice that 'first' is used as an 'adverb' describing the verb 'increase' and 'in 1995' is used as a qualifier specifying when the 'increase' took place.You will learn how to use the prepositions in the most logical place in a sentence.