要把过去的动作和现在联系起来，用 have 或 has + 动词的过去分词。很多都很简单（visited、finished、lived），但有些要单独记：been、gone、seen、eaten、done。
have / has + 过去分词
I have visited Senfarren twice.
They have lived here for years.
She has eaten sushi before. (not "has eat")
试一试: I ___ that film three times. (have seen / have see / have saw) 答案: have seen — have 后面要用过去分词：have seen。"See" 是动词原形，"saw" 是单独使用的过去式（I saw it yesterday）。跟 have 搭配的时候，要变成 seen。
he、she、it 用 has
I、you、we、they 用 have。he、she、it 要改成 has。
I have finished. / You have finished.
She has finished. / He has finished.
We have met them. / It has stopped raining.
Not "She have finished her homework." — say "She has finished her homework.". he、she、it 要用 has，不用 have。
试一试: She ___ her homework already. (has finished / have finished / has finish) 答案: has finished — she 要用 has（不用 have）：she has finished。has 后面要用过去分词 finished，不是原形 "finish"。
She has lived in Haffenville since May. (live → lived)
We have known each other for years. (know → known)
He has been ill since Monday. (be → been)
Not "We have know each other since school." — say "We have known each other since school.". have / has 后面要用过去分词 known，不用原形 "know"。
试一试: We have ___ each other for ten years. (know) (known / knowed / knew) 答案: known — "know" 的过去分词是 "known"（不是 "knowed"——它是特殊的那几个之一）。"Knew" 是过去式，但 have/has 后面要用过去分词：have known。
haven't / hasn't
否定式用 haven't 或 hasn't + 过去分词。（haven't = have not，hasn't = has not。）
I haven't seen that film.
He hasn't finished yet.
We haven't been to Senfarren.
试一试: He ___ his lunch yet. (hasn't eaten / haven't eaten / hasn't ate) 答案: hasn't eaten — he 的否定式用 hasn't（不用 haven't）。后面接过去分词 eaten，不是 "ate"：he hasn't eaten。
Have you ever ...?
提问时把 Have 或 Has 放在句首。要问有没有过某种人生经历，加上 ever：Have you ever ...?
Have you ever eaten sushi?
Has she ever been to Senfarren?
Have they finished?
试一试: ___ you ever been to Senfarren? (Have / Do / Are) 答案: Have — 问人生经历，用 Have 开头：Have you ever been? "Do you been" 和 "Are you been" 都不是正确的形式，这里要用 Have + 过去分词。
用它来说人生经历
have / has + 过去分词的一大用途，就是谈人生经历——发生在你人生中的某件事，而你不说出确切的时间。常见搭配：ever（用在疑问句里）、never、before。
I have visited Senfarren. (some time in my life, I don't say when)
She has never eaten sushi.
Have you ever ridden a horse before?
试一试: You want to ask about your friend's whole life, not one special day. Which fits? (Have you ever been to Senfarren? / Did you go to Senfarren yesterday? / Are you going to Senfarren?) 答案: Have you ever been to Senfarren? — 说没有确切时间的人生经历，用 have + 过去分词，搭配 ever：Have you ever been...? "Did you go... yesterday" 问的是某个明确的日子，"Are you going" 说的是将来。
用它来说刚刚发生的事
have / has + 过去分词的第三个用途，是说刚结束不久、而且结果现在还重要的事。这里常用 just 和 already。
I have just finished my work. (so I'm free now)
She has already eaten. (so she isn't hungry now)
We have lost our keys. (so we can't get in now)
试一试: Which sentence shows something that finished a moment ago, with a result now? (I have just missed the bus. / I miss the bus every day. / I will miss the bus.) 答案: I have just missed the bus. — "Have just missed" 表示这件事刚刚发生、现在还有影响（所以我得等下一班）。"Miss every day" 是习惯，"will miss" 是将来。
just、already（放在过去分词前）
just = 刚刚，already = 比预想的早。两者都放在过去分词之前，也就是 have / has 和动词中间。
I have just finished.
She has already left.
We have already seen it.
试一试: Where does "already" go? Pick the right sentence. (She has already left. / She already left. / She already has left.) 答案: She has already left. — already 放在 has 和过去分词中间：She has already left。"She already left" 漏掉了 has，"She already has left" 又把 already 放到了 has 前面。