GWD30-20

Researchers have announced that the magnetic fields emitted by one manufacturer’s security surveillance system, of which type there are 200,000 worldwide, can interfere with pacemakers and that this interaction can bring on missed or irregular heartbeats, nausea, breathlessness, dizziness, and even fainting.

1. of which type there are 200,000 worldwide, can interfere with pacemakers and that
2. of which, worldwide, there are 200,000 of that type, and which can interfere with pacemakers, and
3. of which type there are 200,000 worldwide, they can interfere with pacemakers and
4. 200,000 of which type exist worldwide, interfering with pacemakers, and
5. 200,000 of that type existing worldwide and can interfere with pacemakers, and

 答案给D，我选A

如果选D的话就是将magnetic fields emitted by one manufacturer’s security surveillance system和this interaction 并列，这样逻辑意思是不通的，因为只有 interaction 可以造成missed or irregular heartbeats, nausea, breathlessness, dizziness, and even fainting.而 magnetic fields 本身是不会造成这些症状的。况且，如果将interfereing with pacemakers作为插入语的话，后面的this interaction是没有指代对象的

A中后面的that 从句和前面的that 从句并列，一起作为announced宾语从句，所以结构很完整

Open to discussion

这题已经讨论过了，答案是A。其它选项都不对。

另外，GWD30有很多SC的答案都是错的。

谢谢，不知香香茶同学是哪里看到讨论的，为什么我怎么也搜不到30套及其他2*套的讨论贴汇总？

没有专门的讨论贴汇总，你直接搜，比如这题，就搜索“30-20”，那么就会有你想找的讨论贴了。前面不用加GWD，加了反而难搜，因为有人加了空格，有人加中杠，有人什么也没加。

good job!