The correct option is C Save
A synonym is a word that is similar in meaning to another.
The given word 'rescue' means 'to save someone from danger or difficulty', for example, 'the girl was rescued from the clutches of the predator'.
From the options, 'save' also means the same: to rescue from harm or danger. (Consider the sentence: the girl was saved from the predator.') Hence it's the synonym of 'rescue' and option D is correct.
'Peril' means danger, it isn't similar to 'rescue'.
Similarly, 'danger' refers to a situation wherein one gets harmed or injured, it is similar in meaning to 'peril'.
'Pitfall' is also similar to 'peril' and 'danger', it means 'a hidden or unsuspected danger'.
These three do not mean the same as 'rescue', hence options A, B and C are incorrect.