请高手帮忙翻译英语，谢谢！

Question

1.他们在火车抵达以前20分钟就已到达车站。(arrive at)

2.有迹象表明此事故是完全可以避免的。(could have done)

3.他是历史专业的学生。（major）

4.只有两门课供你选修。（take）

5.他把一生都贡献给了为人类造福的事业。（office hours）

Answer 1

They had arrived at the train station 20 minutes before the train's arrival.

There have been signs that the accident could have been avoided.

He majors in history./His major is history.

There are only 2 classes for you to take as an elective course.

He devoted all his office hours to the benefit of humankind.

Answer 2

They had 20 minutes before the trains arrive at stations
There are indications that this accident was completely avoidable
He is a professional student of history
Only two classes for your electives
His whole life has been dedicated to the cause for the benefit of mankind

Answer 3

1.they had arrived at the train station twenty minutes before the train's arrival.
2.there's evidence indicating that this accident could have been avoided.
3.he is a history major./he majors in history.
4.you can take only two elective courses.
5.he has devoted all his office hours to the interest of human beings.

Answer 4

1they have arrived at train station before the train arrived.
后面的没时间了不好意思