OFFICIAL EXPLANATION
The reason that John decided not to study for the GMAT is because he felt confident about his quantitative and verbal skills.A. is because he felt confident about his quantitative and verbal skills
This answer choice is stylistically flawed. Using both The reason and because is redundant.
What helps us identify this question as a redundancy question as well as identify this mistake is the following Stop Sign:
B. is that he felt confident about his quantitative as well as his verbal skills
Although this answer choice corrects the originalredundancy (i.e., the use of the reason... because), it is still stylistically flawed: replacing the single word and with the three-word phrase as well as creates redundancy.
What helps us identify this mistake is the following Stop Sign:
Always read through all answer choices before choosing the best one, and remember to eliminate any answer choice that repeat this redundant structure.C. because he felt confident about his quantitative and verbal skills
This answer choice is both stylistically and grammatically incorrect.
The stylistic mistake is using both The reason and because, which creates redundancy.
What helps us identify this mistake is the following Stop Sign:
The reason + because
What makes this sentence grammatically incorrect is that the verb is has been omitted.D. is that he was skillful in both the quantitative and verbal sections
Although this answer choice corrects the original redundancy and is both grammatically and stylistically correct, it changes the meaning of the original sentence: John was skillful and John felt confident are not the same thing.
Also, this answer choice makes unnecessary changes, such as the addition of the word sections and a change in the original word order.E. is that he felt confident about his quantitative and verbal skills
CORRECT