2）He were there / He was there 应该都正确，但是 一般上 是用 He were 的。
Second conditional
- uses the past simple after if, then 'would' and the infinitive:
- The structure is usually: if + past simple（过去式） >> + would /could + bare infinitive（=verb 原字）.
When we use the verb ‘to be’ in the second conditional, the past form is always were and not was for the subjects I, he, she and it.
Note that this use of were is possible and recommended with all subjects. Was is also becoming acceptable, but many grammarians still insist that you should use were. Nowadays you can often hear young native speakers use was instead of were, especially in an informal context.
- If she were my daughter, I wouldn’t let her drop out of school. (NOT If she was my daughter, …)
- If I were you, I wouldn’t trust him.
- If they were really interested in the offer, they would contact you.
1) If I were you, I wouldn't mention it./
倒转顺序：I wouldn't worry if I were you.
（这个例子，I 后用were）
2) If she was prime minister, she would invest more money in schools.（she 后面用 was)
3) He would travel more if he was younger.(he 后面用 was)
4) She would travel all over the world if she were rich.( she 后面用 were)
5) If I were you, I wouldn't go out with that man.
6）If we had a garden, we could have a cat.
7）If I won a lot of money, I'd buy a big house in the country.
In some cases, however, if I was is also possible. For example, when are talking about real situations that happened in the past/giving advice , the use of if I was (or if he /she / it was) is considered more correct.
- If I was in a hurry, I usually skipped my breakfast.
- If she was angry, she would shut herself up in her room.
补充： second conditional 的全部用法：
1.To imagine life is different
1）use it to talk about things in the future that are probably not going to be true. Maybe I'm imagining some dream.(未来不大可能发生的事情）
例子：
She would pass the exam if she ever studied.
(She never studies, so this won't happen)（不学习，怎么可能过关/及格呢。）
2）use it to talk about something in the present which is impossible, because it's not true.（现在不可能发生的事，因为 这些 事情不真实）
例子：
If I had his number, I would call him. (I don't have his number now, so it's impossible for me to call him).
If I won the lottery, I’d buy a house.
2. hypothetical questions
Hypothetical questions to ask someone to imagine what they would do in a different situation. So these situations are not real.（一个假设性问题来提问 某某人 如果遇到不同情况，他们如何面对问题。）
Example:
- What would you do if you quit your job?
- If you won a million dollars, would you travel the world?
- If you only had one day in Singapore, what would you do?
3. give advice
- give advice and if you think about it, when someone asks you for advice, you usually try to imagine what you would do in their situation and share that with them.( 给予意见。当某某人要求你给他们意见，一般想象 在 某种 情况你会怎样做 什么并 分享 给他们。）
Example:
- If I were you, I’d talk to my boss before I quit my job.
- If I were her, I’d break up with him.
4. give reasons why
- give reasons why you can’t do something
Example:
- If I wasn’t so busy, I’d invite you over for dinner. (如果我不忙，我会 邀请你 吃晚餐。）
这个句子表示 我不邀请你吃晚餐的原因。
first conditional 和 second conditional 的差别：
How is this different from the first conditional?
This kind of conditional sentence is different from the first conditional because this is a lot more unlikely.
For example (second conditional): If I had enough money I would buy a house with twenty bedrooms and a swimming pool (I'm probably not going to have this much money, it's just a dream, not very real)
But (first conditional): If I have enough money, I'll buy some new shoes (It's much more likely that I'll have enough money to buy some shoes)
参考资料：
1）https://www.perfect-english-grammar.com/second-conditional.html
2）https://learnenglish.britishcouncil.org/grammar/b1-b2-grammar/conditionals-zero-first-second
3）https://mmmenglish.com/2020/03/26/second-conditional-sentences/
4）https://www.wallstreetenglish.com/blog/second-conditional
