So substantial has been the increase in demand for treehouses that the world's leading treehouse builder will build over 150 treehouses in 2004, up from three in 1996.
A. So substantial has been the increase in demand for treehouses that
B. The increase in demand for treehouses has been so substantial, so that
C. The increased demand for treehouses has been such,
D. Such has the increased demand for treehouses been that
E. Such has been the increased demand for treehouses, that

Inverted structure is used in the first part of the sentence. To simplify, we can also write the question & options as follows-
The increase in demand for treehouses has been so substantial that the world's leading treehouse builder will build over 150 treehouses in 2004, up from three in 1996.
A. So substantial has been the increase in demand for treehouses that - The increase in demand for treehouses has been so substantial that
-Correct use of "So...that"

B. The increase in demand for treehouses has been so substantial, so that - The increase in demand for treehouses has been so substantial, so that
-Use of SO again along with Comma is incorrect (it leads to redundancy)

C. The increased demand for treehouses has been such,- The increased demand for treehouses has been such
- Such WHAT? -> WHAT is missing. Note "The world's......in 1996" in result of previous effect

D. Such has the increased demand for treehouses been that - The increased demand for treehouses has been such that
- Use of SUCH THAT is incorrect. SUCH should be followed by an Adjective to emphasize the effect.

E. Such has been the increased demand for treehouses, that - The increased demand for treehouses has been such, that
- Same error as in option D; moreover, comma should not be used after SUCH.

Hope it helps

Meaning,
The increased demand for tree houses has been such that the world's leading treehouse builder will build over 150 treehouses in 2004, up from three in 1996.

(E) wins

Why do you think the meaning of choice (E) is correct usage?

For me, choice (A) is better. The construction of the sentence here is reverse

(A) The increase in demand for tree houses has been so substantial that the world's leading treehouse builder will build over 150 treehouses in 2004, up from three in 1996

In choice (E) there is no idiom be + such that. You can check it now :D.
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B. The increase in demand for treehouses has been so substantial, so that - wrong idiom
C. The increased demand for treehouses has been such, - awkward
D. Such has the increased demand for treehouses been that - awkward construction
E. Such has been the increased demand for treehouses, that - Changes meaning

A wins

Am

My answer is (A) as well.
Whats OA?
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+1 for A. E seems to be incorrect grammatically.

So substantial has been the increase in demand for treehouses that the world's leading treehouse builder will build over 150 treehouses in 2004, up from three in 1996.

A. So substantial has been the increase in demand for treehouses that
seem good

B. The increase in demand for treehouses has been so substantial, so that
changes meaning completely

C. The increased demand for treehouses has been such,
need that

D. Such has the increased demand for treehouses been that
such is not specific enough

E. Such has been the increased demand for treehouses, that
comma is wrong after treehouses

Here is the Official Explanation from Kaplan

Answer A - The proper construction would be "So substantial has been X that Y" or "So substantial has X been that Y" or "X has been so substantial that Y." (A) is the only choice that uses one of these correct options.

(B) is redundant because it uses "so" twice for the same purpose.

(C), (D) and (E) are all unidiomatic.

first of all few things to note
1) So that
2) Such that
3) So [adjective] that
4) Such [noun] that
all the above four forms are correct. please don't comma between so that or such that. putting comma will make the sentence wrong
With this in mind let's see the options

A. Correct So substantial has been the increase in demand for treehouses that
The entire green part works as an adjective
B. Incorrect The increase in demand for treehouses has been so substantial, so that
Wrong Idiom
C. Incorrect The increased demand for treehouses has been such,
Wrong idiom
D.Incorrect Such has the increased demand for treehouses been that
Clause between that is wrong
E. Incorrect Such has been the increased demand for treehouses, that
Wrong Idiom

Can any one please explain why the use of such that in D is wrong and if wrong then how such that could be used in that sentence?

B) is redundant because it uses "so" twice for the same purpose.

(C), (D) and (E) are all unidiomatic.

A is the correct answer.

+1 for A. The usage of So...That is correct .
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So substantial has been the increase in demand for treehouses that the world's leading treehouse builder will build over 150 treehouses in 2004, up from three in 1996.

A. So substantial has been the increase in demand for treehouses that
so that clause works. meaning poper. Correct
B. The increase in demand for treehouses has been so substantial, so that
so,..so that. wrong
C. The increased demand for treehouses has been such,
"such,..?"
Wrong
D. Such has the increased demand for treehouses been that
concentrating on 'increased demand' not on 'demand' increase. Wrong.
Meaning distorted

E. Such has been the increased demand for treehouses, that
concentrating on 'increased demand' not on 'demand' increase. Wrong.

I think this question was made during 2004 . The structure is as if the person is present in 2004 and talking about the demand increase till then.
I choose A - direct answer
So... that...
Such .... that. . - meaning change.
In E I don't like "," before "That".
because of above two reasons i reject E. Only A prevails.

Hence answer is A.

The sentence as written contains no grammatical errors. So substantial has been X that Y is an accepted construction. Other acceptable forms would be So substantial has X been that Y, or X has been so substantial that Y. There is no reason for the correct answer to switch to one of these other forms, but be aware that it could do so.

A quick scan of the choices doesn't reveal any useful grouping. Proceed to take a closer look at the choices.

(B) creates a redundancy by using "so" twice for the same purpose. (B) would have been fine had it said, The increase in demand for treehouses has been so substantial that.... As is, however, (B) must be eliminated.

(C) makes no sense when read into the sentence: "The increased demand ... has been such, the world's leading...." The sentence is now missing a connector between the first clause and the second. Eliminate (C).

(D) and (E) use "such ... has been" incorrectly. The phrase such has beenis used to mean this is how things are, not to convey that the quantity of something is great enough to lead to a certain result. For example, the phrase is used correctly in Such has been my life, or Such has been the history of this country. With this question, however, the sentence is trying to say that the increase in demand has been great enough to lead to much more work for the leading builder. "Such ... has been" is therefore inappropriate here. Eliminate (D) and (E).

Posted from my mobile device
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Can anyone post the correct usage of such that in GMAT?

Thanks