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 effectD. 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