语法填空最容易丢分的 5 个位置——介词后加 ing、than 用比较级，一次理清
引言
语法填空丢分，往往不是因为语法不会，而是没注意到空格前后的"信号词"。看到 than 不知道用比较级，看到介词不知道后面动词要加 ing，白白丢分。
这篇文章把语法填空最容易丢分的五个位置列出来，每个位置配判断方法和例题。
易错点一：介词后面的动词
信号：空格前面有 in / on / at / by / with / about / without / after / before
规则：介词后面的动词一律加 ing
```text
错：He is good at play basketball.
对：He is good at playing basketball.
错：Thank you for help me.
对：Thank you for helping me.
错：I'm interested in learn English.
对：I'm interested in learning English.
```
特别注意：spend time doing / be used to doing / by doing，都是这个规律。
易错点二：than 前面的比较级
信号：空格后面有 than
规则：填形容词或副词的比较级
```text
短单词加 er：tall → taller, fast → faster
长单词前面加 more：difficult → more difficult
不规则：good → better, bad → worse
```
```text
错：She is tall than her sister.
对：She is taller than her sister.
错：This book is interesting than that one.
对：This book is more interesting than that one.
```
易错点三：the 后面的最高级
信号：空格前面有 the，句意表示"最……"
规则：填最高级
```text
短单词加 est：tall → tallest, fast → fastest
长单词前面加 most：beautiful → most beautiful
不规则：good → best, bad → worst
```
```text
错：This is the better book I have ever read.
对：This is the best book I have ever read.
```
注意：the + 序数词也是固定用法（the first / the second / the third）。
易错点四：形容词和副词混用
信号：空格在主语和谓语之间，或者修饰动词
规则：用副词，不是形容词
```text
形容词修饰名词：a quick runner
副词修饰动词：run quickly
```
```text
错：She runs quick.
对：She runs quickly.
错：He is a carefully driver.
对：He is a careful driver.（修饰名词用形容词）
```
变化规则：
```text
一般直接加 ly：quick → quickly
y 变 i 加 ly：happy → happily, lucky → luckily
特殊：good → well
```
易错点五：名词单复数
信号：空格前面有 one of / several / many，或者前面没有冠词
规则：名词用复数
```text
错：one of my friend
对：one of my friends
错：several student
对：several students
```
复数变化：
```text
一般加 s：book → books
辅音 + y 变 i 加 es：city → cities
s/x/sh/ch 结尾加 es：bus → buses, box → boxes
```
总结
五个易错位置的信号词：
```text
看到介词 → 后面动词加 ing
看到 than → 前面用比较级
看到 the + "最" → 用最高级
修饰动词 → 用副词（加 ly）
one of / several / many → 名词用复数
```
```text
今日小抄：
at playing 介词后加 ing
taller than than 前用比较级
the best the 后用最高级
runs quickly 修饰动词用副词
one of friends one of 后用复数
```