4. 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

1．平行结构：平行结构的形式对称  the only way to … is to …

2．单复数一致：代词要和他指代的名词的数一致。 Them/it 的选择
Citrus 单复数都可以，这里用单数，因为指一类
it is better to use the singular in referring to an anatomical feature common to an entire species;这是ets对og167的

3．代词正确答案的标志：当前面有多个名词可以指代的时候，通常补出概括性的名词来去掉代词，防止歧义。

4．句子逻辑意思：用 when 引导的时间状语从句只强调动作发生的时间上的同步，没有强调因果的意思。表示因果/目的，可以用不定式。A and B，当 A/B 是两个连续的动作的时候，可以存在强调因果的意思在。   

5．习惯用法Before / after …. When 连用不符合语言习惯

6．Rot 的用法 既可以是及物动词又可以是不及物动词