During the 1920s, the U.S. stock market

Question

During the 1920s,  the U.S. stock market had undergone rapid expansion, reaching its peak in August 1929, and by then the production already declined, and unemployment rose , leaving the stocks in great excess of their real value.

A. the U.S. stock market had undergone rapid expansion, reaching its peak in August 1929, and by then the production already declined, and unemployment rose

B. the production had already declined with the rising unemployment, by the time the US stock market underwent rapid expansion reaching its peak in August 1929

C. the U.S. stock market underwent rapid expansion and thereby reached its peak in August 1929, and by then the production had already declined, and unemployment had risen

D. the U.S. stock market reached its peak in August 1929 after undergoing rapid expansion, and by that time the production had already declined, and unemployment had risen

E. with the production already declined and the unemployment already rising, the US stock market underwent rapid expansion, reaching its peak in August 1929

generis 
 AjiteshArun 
 GMATNinja

I do not understand why choice D is wrong here. please help me understand. Thanks

BoundMan · Answer

generis 
Thank you for your reply.
Isn't the option C doing the same.
an economy both undergo rapid expansion such that it reached its peak AND 
by that time (at that time) 
production simultaneously declined and unemployment rose

generis · Answer

akash7gupta11  yes, I think so.

I think you're right. I changed my mind. 
Shoot! I just deleted my reply rather than editing it.

On the other hand . . .
 akash7gupta11  
In option D, it would be better if  after undergoing rapid expansion  were placed before  stock market reached its peak  because "by that time" seems to be referring  expansion  (at which point simultaneous signs of contraction seem weird).

If we move  undergoing rapid expansion  so that it describes only the stock market's expansion over a period of time during the 1920s (growth that peaked in 1929), then we are left with the correct impression that  contraction  in other sectors had begun to occur separately and simultaneously.

What's the source?

BoundMan · Answer

generis  one of my whattsapp friend told me that option D may be an awkward construction. What do you think?

Please notice the dates here, 1920 and 1929.
 During the 1920s, the U.S. stock market reached its peak in August 1929

generis · Answer

akash7gupta11  your friend is correct.

In fact (where is my coffee?) the first part of option D's first clause is silly. 
 During the 1920s, the stock market reached its peak in August 1929.  
First, "during the 1920s" and "in August 1929" do not work together. The pairing is incoherent.

Second, we need "after undergoing rapid expansion" to come right after  During the 1920s  (and as mentioned, right before  the U.S. stock market reached its peak ). 
Constructed that way (as in C), expansion happens  during  the 1920s (a time  period ) and reaches its peak in 1929 (a specific point in time).

This is   the sequence   that C gets right and that D scrambles:
 
stock market underwent rapid expansion 
and
after that expansion
the market peaked in 1929

and by that time
production had (already) declined
and
unemployment had (already) risen

People who drove the stock market's expansion were not paying attention to signs of danger in the economy.

BoundMan · Answer

generis  Thank you. The source is egmat

ayushkumar22941 · Answer

how is option a wrong ? how is c better than a ?

generis · Answer

ayushkumar22941  , this question tests a common pattern in English, though I have not seen a lot of discussion about this pattern.

Three phrases show up in the options
 Y, by the time X 
X, and by that time, Y
X, and by then, Y

All three phrases generally mean "when" X happened—and that Y events occur before X.

Certain phrases indicate that verb tenses should shift in a sentence. Among those phrases are  by the time, by that time,  and  by then.

By then  tells us that the verb tense should change, in this instance from simple past to past perfect.

That is,  by then  indicates that there was a sequence of events. 
Production and employment declined  before  the stock market reached its peak in August 1929. That shift in time is communicated by shifting the verb tenses.

X, and by then Y

THIS thing happened, and  by then  THOSE things  had  happened.

The sequence in (A) does not follow the logic of the phrase 
  X, and by then Y,   
in which   Y happens  before  X   
and thus in which
(1) we should write    X in simple past tense,   and
(2) we should write   Y in past perfect tense.

Past perfect is called "the past of the past." The X event is one discrete moment in the past (simple past).
The Y events that occur before that X event are thus the past of that marked-off (X) past.

X = stock market at its peak
Y = production down, unemployment up

(A) uses tenses for the events in the sequence that are exactly backwards.

Backwards  
-- In A, X is partly rendered in past perfect:
the market 
 had undergone  rapid expansion...

Worse, the really important time marker, the stock market's peak, does not have a working verb: 
   reaching  its peak in August 1929. 
 Reaching  is a present participle (verbING), not a working verb. (A) does not render the X event in simple past tense as it should.

-- Further, in A, the Y events ARE rendered in simple past tense  declined  and  rose . Incorrect. Y events should be written in past perfect tense.

Option C, by contrast, correctly follows  X (simple past), and by then Ys (past perfect).

...   reachED its peak, and by then the production had already declined, and unemployment had risen ...

The simple past event followed by "and by then" sets up the shift of verbs to past perfect (to had verbED).

Think of the "by the time" phrases as similar to idioms. The phrases are signals that verb tenses must shift in a particular way.

Hope that helps.

** All three "by" phrases used in this question tell us explicitly to shift tenses. 
Though they are arranged differently, they mean the same thing. All three signal a verb tense shift.

I just skimmed a few OGs. On the GMAT you are likely to see the phrase
 By the time X, Y. 
That word arrangement simply inverts  Y, by the time X  that we see in (B).

Reading examples helps cement the pattern.

By the time X, Y. 
The Y events occur before the X event.
X gets simple past tense. Y gets past perfect.

By the time THIS thing happened, THAT thing  had  happened.

THAT thing had happened by the time THIS thing happened.

By the time he found his wallet, he had looked in ten places.

He had looked in ten places by the time he found his wallet.

X, and by then Y

THIS thing happened, and by then THAT thing had happened.

He found his wallet, and by then he had looked in ten places.

X, and by that time Y

THIS thing happened, and by that time THAT thing had happened.

He found his wallet, and by that time he had looked in ten places.

(BTW,  the  should not precede  production,  but the error in an otherwise good question is in all options and is not a decision point.

amitanshumaity · Answer

During the 1920s, the U.S. stock market had undergone rapid expansion, reaching its peak in August 1929, and by then the production already declined, and unemployment rose, leaving the stocks in great excess of their real value.

Understanding the intended meaning and structure of the sentence can help immensely I guess.

Meaning analysis--> 1920s : US market was undergoing rapid expansion. Reached its peak on Aug 1929.
 By then--> by the time it's stock market reached its peak
 Which means the next events which follow must have happened earlier in the past and Past perfect tense 
 should be used.

Now, between Choice C and D.

C. the U.S. stock market underwent rapid expansion and thereby reached its peak in August 1929, and by then the production had already declined, and unemployment had risen

D. the U.S. stock market reached its peak in August 1929 after undergoing rapid expansion, and by that time the production had already declined, and unemployment had risen

We already know from the meaning analysis that it was the rapid expansion which resulted in the stock market to reach its peak in 1929.
Rapid expansion --> Peak in 1929.

Note the diction in choice D.

the U.S. stock market reached its peak in August 1929 after undergoing rapid expansion.

It talks about reaching the peak first then undergoing rapid expansion. ( Not a detrimental error, but definitely not the best of a lot)
( GMAT always prefers better Diction, from what I know).

Also, in a sentence where interrelated events in the past are connected, you should select the choice that conveys the meaning in the best manner, which in our case is choice C.

abhi2707 · Answer

DO NOT IGNORE the non-underlined part...
Between C and D
1. D: During 1920, US Market etc etc in Aug 1929....NON SENSE
2. C: first clause ends in 1929, and  by then  makes a better proposition as far as concision is concerned

Is there anything else?

gvij2017 · Answer

Do I need past perfect tense if I am using sequence modifier.

That is, by then indicates that there was a sequence of events.

VerbalBot · Answer

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During the 1920s, the U.S. stock market

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