I cant tell you the exact answer without the answer choices but commonly used formats include MLA, APA, and AMA. hope this helps!
It adds emphasis shows how common it is for them
Vain is the correct answer. Plug in each word given into the sentence and then read it to see if the sentence makes sense.
"We may try in credibility to solve our problems on our own.." Credibility is incorrect.
"We may try in predict to solve our problems on our own.." Predict is incorrect.
"We may try in forgive to solve our problems on our own.." Forgive is incorrect.
"We may try in vain to solve our problems on our own.." Vain is correct!
Hope this helps! (:
