OG12_SC004_Explained!

Of all the vast tides of migration that have swept through history, maybe none is more concentrated as the wave that brought 12 million immigrants onto American shores in little more than three decades.

(A) maybe none is more concentrated as
(B) it may be that none is more concentrated as
(C) perhaps it is none that is more concentrated than
(D) maybe it is none that was more concentrated than
(E) perhaps none was more concentrated than

Explanation:

Concept one:

X is more ......................than Y, 

Where X and Y MUST be grammatically parallel.

When we see "More" , we must search for "Than" because "More than" is correct.

The followings are WRONG:

X is more .........................AS Y

Elimination: The options A and B have used "More ........as", which is wrong. They are eliminated.

Concept Two:

It is none that is/was can be replaced by shorter alternative "none is/was"; GMAT prefers shorter sentences. 

In the options C and D, "it is none that is/was" is redundant. We can eliminate C and D.

Answer: E

OG12_SC003_Explained

Although various eighteenth- and nineteenth-century American poets had professed an interest in Native American poetry and had pretended to imitate Native American forms in their own works, until almost
1900, scholars and critics did not begin seriously to study traditional Native American poetry in native
languages.

(A) until almost 1900, scholars and critics did not begin seriously to study
(B) until almost 1900 scholars and critics had not begun seriously studying
(C) not until almost 1900 were scholars and critics to begin seriously to study
(D) it was not almost until 1900 when scholars and critics began to seriously study
(E) it was not until almost 1900 that scholars and critics seriously began studying

Explanation:
Concept one:
Clause, Adverb, Clause makes the problem.
Example:
Though she had scored higher, in 1990, the score is no more valid. 
Now, we have a confusion about the position of "in 1990". It has two meanings:
1. She had scored higher in 1990.
2. The core is not valid in 1990.

Conclusion: The structure "Clause, Adverbial phrase, clause" creates an ambiguous sentence.

Elimination: This rule eliminates the option A.

 Concept Two:

 We cannot use two past perfect tense in the same sentence.
We can use: 

Perfect+ Simple Past => They had reached the station before the train left.
Simple Past + Past perfect=> They came after the train had left.

Elimination: This rule eliminates the option B.

Concept Three:

Memorize the following rule. [Take note.]

To Begin + To Study  is WRONG

 I have searched google by "to being to study", and I have found the following search results:

To begin study

To begin a study

To begin studying

To begin your study

To begin the study

Began to study

--> All these sentences are CORRECT.

This implies that the form "To BEGIN to STUDY" is WRONG.

Elimination: This rule eliminates C

Concept Four:

Almost until 1990 is not idiomatic.

--> Almost should modify 1990, but in the present form it is in a remote place to modify 1990. 

--> Almost 1990 means around 1990. Almost until 1990 creates a vague modification. 

--> Until almost 1990 is okay in this sense.

Elimination: This rule eliminates D. 

Answer: E.