buy：过去式bought，过去分词bought；say：过去式said，过去分词said；think过去式thought，过去分词thought；feel过去式felt，过去分词felt。
不规则的各种变化
词例：
| 动词原形 | 过去式 | 过去分词 | 意思 | 动词原形 | 过去式 | 过去分词 | 意思 |
|---|---|---|---|---|---|---|---|
| pay | paid | paid | 付钱 | lay | laid | laid | 下蛋 |
| say | said | said | 说 | bring | brought | brought | 带来 |
| buy | bought | bought | 买 | fight | fought | fought | 战斗 |
| think | thought | thought | 思考 | sleep | slept | slept | 睡觉 |
| feel | felt | felt | 感觉 | keep | kept | kept | 保持 |
| sweep | swept | swept | 扫 | stand | stood | stood | 站 |
| understand | understood | understood | 理解 | win | won | won | 胜利 |
| catch | caught | caught | 抓住 | teach | taught | taught | 教 |
| find | found | found | 发现 | get | got | got | 得到 |
| hold | held | held | 握 | leave | left | left | 离开 |
| make | made | made | 制造 | meet | met | met | 遇见 |
| shoot | shot | shot | 射击 | dig | dug | dug | 挖 |
| smell | smelt / smelled | smelt / smelled | 嗅，闻 | shine | shone / shined | shone / shined | 发光 |
| sit | sat | sat | 坐下 | have | had | had | 有 |