语法总结
与过去事实相反的虚拟语气
If the Houses of Parliament had not been burned down..., the clock would never have been erected. 用来说明大本钟诞生的历史前提。
相似句：
- If the bridge had not collapsed, traffic would have continued.
- If he had not helped us, we would have failed.
have sth. done
have the clock checked twice a day 表示“安排别人去检查”。
相似句：
- She has her car serviced every month.
- We had the roof repaired last year.
not only ... but ... as well
用来并列介绍大本钟“又大又准”的双重特点。
相似句：
- He is not only clever, but hard-working as well.
- The room was not only small, but dark as well.