一个代词指代问题

moderation

By the same techniques used for genetically enhancing plants,making them disease- or pest-resistant ,researchers have been able to increase the amount of protein in potatoes,sweet potatoes, and tobacoo.

With the same techniques to genetically enhance plants,so that they are disease- or pest-resistant ,researchers have been able to increase the amount of protein in potatoes,sweet potatoes, and tobacoo.

Employing the same techniques used for genetically enhance plants so that they are disease- or pest-resistant ,researchers have been able to increase the amount of protein in potatoes,sweet potatoes, and tobacoo.

这三句话中粗体的they 或them在语法上分别指代什么啊？提醒：前面两句是有逻辑错误的。

谢谢！

you5460

By the same techniques used for genetically enhancing plants,making them disease- or pest-resistant ,researchers have been able to increase the amount of protein in potatoes,sweet potatoes, and tobacoo.

夹心饼干,红字部分可能修饰逗号前也可能修饰逗号后的接近名词,这里就存在它了能既修饰plants 又可修饰 reserchers的情况.

With the same techniques to genetically enhance plants,so that they are disease- or pest-resistant ,researchers have been able to increase the amount of protein in potatoes,sweet potatoes, and tobacoo.

ETS一般忌用WITH.做伴随状语.且so that 一般不用独立在逗号后的分句中.正确的是SVO so that ....

Employing the same techniques used for genetically enhance plants so that they are disease- or pest-resistant ,researchers have been able to increase the amount of protein in potatoes,sweet potatoes, and tobacoo.

我怎么觉得没一句是对的>这里的FOR也有问题,应该用TO表目的吧

linlin2008

三句里的代词指代的都是PLANTS.从句意可以判断,后面的disease- or pest-resistant只能指PLANTS