Question

2009高考英语~~~ 天津卷 15题解析~~~~

This printer is of good quality. If it _______ break down within the first year, we would repair it at our expense.
A. would B. should C. could D. might
考查虚拟语气用法。前句表示打印机质量好，按道理起初的一年内不可能毁坏，所以下句提出了一种将来的可能性不大的假设，由此判断为与将来事实相反的假设，用虚拟，从句形式Be to do, 动词过去时；should 动词原形。故选B.

其中“从句形式Be to do, 动词过去时；should 动词原形”这句话理解不能，望解答O(∩_∩)O谢谢~

Answer 1

这是if引导的条件状语从句中虚拟语气的语法规则。
即：如果是对将来情况的虚拟，则主句的谓语动词由“would/could/might + 动词原形”构成，而if从句的谓语可以使用以下三种结构中的任意一种：
1. 过去式（be动词改成were）
2. were to do sth
3. should do sth
也就是说此题的答案既可以是：if it broke down within the first year，也可以是：if it were to break down within the first year，还可以是：if it should break down within the first year.
should可以翻译成“万一”的意思。

再如：If it rained tomorrow, I would stay at home.
= If it were to rain tomorrow, I would stay at home.
= If it should rain tomorrow, I would stay at home.

Answer 2

should 强调事件的“不可能性”
should，本意“应该”——其实这里有一种商家的责任和保证在内，它‘不应该’在一年内就坏
If it should break down 如果（在很不可能的情况下）发生任何故障......
哪里有 be to do。解答有错就不要信，要相信自己的直觉。

Answer 3

从句Be to do.? 你确定你的提问没打错？理解不能？