英语翻译They will do what they believes in _____________________

They will do what they believes in (irrespective of whether you agree or disagree with their statement ）
The doctors were troubled by （the emergence of a new type of disease among the patients,）
(a doom was slowly befalling the town) and everything began to change.
We were curious ( about how these people had maintained their strong friendship) for so long.
There are many different answers you can give, (and these answers will reveal a particular aspect of yours)
It is well-known that （our mother nature is facing a serious problem of air pollution）.(In order to pass the examination, he studies very hard everyday)
（Whether you like it or not, you must admit that he is right.）