prep-124-their的困惑

124.       (31091-!-item-!-188;#058&004372)

Whereas the use of synthetic fertilizers has greatly expanded agricultural productivity in many parts 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

Ａ中的第一个their为什么肯定的说指synthetic fertilizers 呢，这里又不是从句主语优先指代主句主语～指前面的复数名词parts也有可能嘛～第二个their也有可能就近指代problems~~

很困惑～望牛牛们指教～

(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

(A) 正确，such as用以举例；and连接并列的句子。

恩～到了熏衣紫草ＭＭ的境界了～

谢谢aeoluseros的耐心回答～