语法点：used to / would / be used to (Past Habits)
used to + 动词原形 表示过去经常做而现在不再做的事，或过去存在而现在不存在的状态，强调“今非昔比”。would + 动词原形 也能表示过去反复的动作，但只能用于动作，不能用于状态，而且通常要有明确的过去时间背景。be used to + 名词/动名词 是另一个完全不同的结构，意思是“习惯于……”，used 在这里是形容词，to 是介词。本课第 1 句的 used to sit 和第 2 句的 would bark 就是前两种用法。
结构
| 形式 | 结构 | 例子 |
|---|---|---|
| used to 肯定 | 主语 + used to + 动词原形 | Rex used to sit outside the gate. |
| used to 否定 | 主语 + did not use to / used not to + 动词原形 | Rex did not use to open the gate. |
| used to 疑问 | Did + 主语 + use to + 动词原形? | Did Rex use to bark? |
| would（过去反复动作） | 主语 + would + 动词原形 | He would bark until someone opened the gate. |
| be used to（习惯于） | 主语 + be / get used to + 名词 / doing | Rex is used to opening the gate. |
课文中的例句
- [句 1] Our dog, Rex, used to sit outside our front gate and bark. — used to + 动词原形，表示过去的习惯，现在不再这样
- [句 2] Every time he wanted to come into the garden he would bark until someone opened the gate. — would 表示过去反复发生的动作，有 every time 的背景
- [句 3] …my husband spent weeks training him to press his paw on the latch… — 对比：训练之后旧习惯改变了，说明 used to 的“今非昔比”
- [句 7] Since then, he has developed another bad habit. — 新习惯用现在完成时，与 used to 表示的旧习惯形成对比
补充例句
- My husband used to open the gate for Rex every morning. 我丈夫过去每天早上都替雷克斯开门。
- When Rex was a puppy, he would bark at every visitor. 雷克斯还是小狗时，见到每个客人都会叫。
- The neighbours are used to the noise now. 邻居们现在已经习惯这种噪音了。
易错点
- ❌ Rex is used to sit outside the gate. → ✅ Rex used to sit outside the gate. 表示“过去常常”不加 be，直接 used to + 动词原形。
- ❌ Rex used to sitting outside the gate. → ✅ Rex used to sit outside the gate. used to 后接动词原形；be used to 才接 doing。
- ❌ Rex would be an expert at opening the gate. → ✅ Rex used to be an expert at opening the gate. would 不能表示过去的状态，状态只能用 used to。
- ❌ Did Rex used to bark? → ✅ Did Rex use to bark? 疑问句和否定句中助动词 did 后用原形 use。