Synonym - a word or phrase that means exactly or nearly the same as another word or phrase in the same language, for example shut is a synonym of close.
Antonym- a word opposite in meaning to another
I am not sure if you are doing the same quiz as the other girl but this was her answer: Like a pig or a dog with ultra-sensitive nasal hairs, he was trying to pick up a scent. "He could smell something". Alternatively, his nostrils quivered as he took in air in readiness for an action, so possibly a preparation for an act of aggression.
Answer:
the last one is the correct one