The only way for growers to salvage frozen citrus is to process them quickly into juice concentrate before they rot when warmer weather returns.
(A) to process them quickly into juice concentrate before they rot when warmer weather returns
(B) if they are quickly processed into juice concentrate before warmer weather returns to rot them
(C) for them to be processed quickly into juice concentrate before the fruit rots when warmer weather returns
(D) if the fruit is quickly processed into juice concentrate before they rot when warmer weather returns
(E) to have it quickly processed into juice concentrate before warmer weather returns and rots the fruit
Some thoughts:
1. Think about the pronouns used in the underlined portion of the sentence as soon as you get.
=> We can see the two pronouns: "them" and "they".
2. Look for the unambiguous reference for the pronouns used in the underlined portion:
=> The nouns used in the previous part of the sentence are "the way", "growers", and "frozen citrus".
3. Match the nouns with the literal meaning of the sentence:
=> To process the way. OUT. [Way can not be processed.]
=> To process the growers. OUT. [Growers can not be processed.]
=> To process the citrus. Correct. [Citrus can be processed.]
4. Match the numbers of the pronouns and the nouns:
=> Citrus is singular, but "them" is plural.
So, all the options that use "them" or "they" are NOT correct.
=> From this rule we can eliminate A, B, C, and D.
The only option that remains is E, the best answer.
Another TIP:
"The only way to do something is TO do......." is the correct structure. So, we are in between A and E.
Look to the option A:
(A) to process them quickly into juice concentrate before they rot when warmer weather returns.
=> They rot. The warmer weather returns. From A, it seems that the two sentences are separate. Actually, it is the warmer weather that rots, and it should be expressed in the sentence. Option A fails to do so.
So, only option E remains.