Q20:

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

 Answer: D

看了以前的讨论，还是不太清楚，请大家帮帮忙解释一下。

我选了A. 

觉得 主句主语announce 后面接了两个that clause, 比较合理，而且前一个clause里主语谓语也都齐全

但是D, and 后面是一个完整的从句，而前面一个应该与其并列的从句却没有了谓语，所以觉得D不对。

 agree with you,

A is correct.

顶．希望讨论出一个结果来．

我看的ｇｗｄ分类解释说是Ｄ选项中， the magnetic fields and　this interaction 并列做ｔｈａｔ从句的主语．觉得这种表达很怪，这种解释很牵强．