With corn, soybean, and wheat reserves being low enough so a poor harvest would send prices skyrocketing, grain futures brokers and their clients are especially interested in weather that could affect crops.
(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. The question can be accessed at GMAT Club)
The sentence begins with a prepositional phrase (with corn…skyrocketing) modifying the main clause (grain futures…crops).
Grain futures brokers and their clients are very interested in weather that could affect the harvest of crops. Why are they interested? Because the reserves of corn, soybean, and wheat are quite low. How much low? Low to the extent that a poor harvest would make the prices extremely high. (Therefore, the brokers are interested in knowing whether there’s going to be a poor harvest)
Now, we understand that “a poor harvest would send price skyrocketing” is providing information about the extent of “low” levels of reserves. The correct and most concise way to express such relationship is using the idiom ‘so X that Y’ i.e. “so low that a poor harvest…” in option C.
(A) Incorrect. The structure “low enough so” is non-idiomatic.
(B) Incorrect. This option combines two idiomatic structures “so X that Y” and “X such that Y”, producing a non-idiomatic structure “so X such that”.
(C) Correct. As explained in the sentence analysis.
(D) Incorrect. “low enough so” is non-idiomatic. The use of relative clause “that are” unnecessarily makes the option wordy.
(E) Incorrect. “so low such that” is non-idiomatic. The use of relative clause “that are” unnecessarily makes the option wordy.