I think it is very important to have fun at study English.  →  I think it is very important to have fun when you study English.​

We improve our skills the fastest when we enjoy something.   →  We improve our skills the fastest when we enjoy doing something.​​

-넌 어떻게 먹고 사니?

What do you do for a living?   →​ How do you make a living?

=> Another way: Your sentence is correct and this is another way of saying it.

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-아내가 임신했어요.

My wife got pregnant. →​​ My wife is having a baby.

=> Another way: Your sentence is correct and this is another way of saying it.​

-나는 그가 약속을 지키지 않아서 화가 났다.

I was mad that he didn't keep promise.​ →​​​She was upset because he didn't keep his promise.