[求助]一个纠结的代词多重指代问题

我看到prep笔记引用白勇还是刘振民书里的关于代词多重指代的说明是这样的

代词（比如：they）在出现多重指代的时候，原则是就近指代。XDF曾经说：they/he/she/it在出现多重指代的情况时，要优先指代与其位置相同的对象，S指代S，O指代O。后来，又看到prep上说的是，当两个句子并列时，其中一个句子主语为代词的话，那么它肯定指代的是另一个句子中的主语。

于是，我自己得出了这样的结论：

前提是代词出现多重指代的情况：当两个句子连接在一起时（主从连接和主主并列都可以），they/she/he/it优先指代与其位置相同的对象，也就是说，只有这几个代词放在句子中的时候，这个优先指代才会产生；而当这些代词不是在上述情况中出现时，出现多重指代就采取就近指代的原则。

大家帮忙看看我推测的对不对，马上就要考试了，但是发现自己语法看的东西越多，做题的时候想的就越多，做题结果就越不理想。

同问！ 谢谢！

再多问一个：

同样的代词出现在同一句子里，是指代同样的词，还是可以分别就近指代呢？ 比如，这道题的c选项：

of the world, an increase in their use can create serious environmental problems such as water

pollution, and their substitution for more traditional fertilizers may accelerate soil structure

deterioration and soil erosion.

(A) an increase in their use can create serious environmental problems such as water pollution, and

their substitution for more traditional fertilizers

(B) an increase in their use can create serious environmental problems like water pollution, and if

substituted for more traditional fertilizers, it

(C) if these fertilizers are used increasingly, they can create serious environmental problems such

as water pollution, and if used as substitutions for more traditional fertilizers, they

(D) the increased usage of these fertilizers can create serious environmental problems such as

water pollution, while if substituted for more traditional fertilizers, this substitution

(E) the increased usage of these fertilizers can create serious environmental problems like water

pollution, while their substitution for more traditional fertilizers