Synonyms can be expressed in a sentence like: “A is another word for B and C is another word for D”.
Examples of synonyms are easy-simple, teach-instruct, smart-clever, quietly, silently etc.
An analogy based on antonym can be expressed in a sentence like “A is opposite to B and C is opposite to D”.
Examples of antonyms are big-small, first-last, more-less, laugh-cry, light-dark, wet-dry, good-bad, fat-thin, smart-dumb, etc.
Tip: These types of exercises often also test word knowledge. Especially with synonyms it will often be a more difficult word for the same thing. Pay close attention to this relationship if you see difficult words among the possible answers.