介词短语是完形填空和语填的暗考点：in time 与 on time 差一个介词，意思从「及时」变成「准时」。这类搭配没有道理可讲，只能按清单精准记忆，这篇把最常考的整理成一表。
高频介词短语对照表
| 短语 | 含义 | 例句 |
|---|---|---|
| in time / on time | 及时（来得及）/ 准时（不迟到） | We got there just in time. / The train arrived on time. |
| at first / at last | 起初 / 最后 | At first he disagreed, but at last he agreed. |
| in fact / in the end | 事实上 / 最终 | In fact, he is a kind man. |
| at once / right away | 立刻 | Do it at once. |
| by accident / on purpose | 偶然 / 故意 | I met her by accident. He broke it on purpose. |
| in addition / in public | 此外 / 公开地 | In addition, the price is low. Don't shout in public. |
| on business / by heart | 出差 / 靠记忆 | My father is away on business. Learn the poem by heart. |
动词与介词的固定搭配
- be interested in 对……感兴趣；be good at 擅长
- be famous for 因……出名；be famous as 以……身份出名
- agree with 同意某人；agree to 同意某事（计划、建议）
- arrive in + 大地点；arrive at + 小地点
- be made of / from：of 看得出原料，from 看不出原料
- look forward to + doing（to 是介词）；be used to doing 习惯于
记忆策略：介词短语按「介词分组」比按字母表背快得多——in 系、on 系、at 系、by 系各收一组，考场上按介词联想检索。
易错点：look forward to 后面接 doing 不是原形
I look forward to hear from you 是写作和改错题里出镜率最高的错误之一：这里的 to 是介词，不是不定式符号，后面必须接动名词——I look forward to hearing from you。同类介词型 to 还有 be used to doing、devote ... to doing、pay attention to doing。判断方法背一条铁律：见到这几个短语里的 to，一律当作介词处理，后面动词必须加 ing。语法填空给动词提示时，先查空格前是不是这类短语，是就直接填 doing 形式。