哪种形式可完成 “What would our lives be if X-ray machines ...”？

问题

What would our lives be if X-ray machines ...

答案选项

1. were not invented
2. would not have been invented
3. had not invented
4. had not been invented

答案

had not been invented — option 4.

解释

这个条件涉及一个过去发生的事件：X 光机的发明。对不真实的过去条件应使用 Past Perfect。由于机器承受“发明”这个动作，因此需要被动语态：

had not + been + invented。

补全后的句子是 What would our lives be if X-ray machines had not been invented? 这个结果描述了我们生活的一种假设状态，而条件则设想了不同的过去。