1:"我想当工程师".2“和好朋友起度过过生日”3：“语法最难，因为它难理解”

1:"我想当工程师".
I want to be an engineer.
2“我和好朋友一起度过生日”
I spent the time celebrating my birthday with my good friend.

3：“语法最难，因为它难理解”
Grammar is the most difficult,because it's hard to understand.

I want to be an engineer.
to celebrate my birthday with my good friends
Grammar is most difficult/challenging because it is hard to understand.