A synonym is a word that is similar in meaning - the correct answer is A. "speak" and "talk" are synonyms.
The other answers can be confusing, I will explain why:
B: pronounced the same : this is a homonym. For example, "write" and "right" are homonyms.
C: these are antonyms: for example big and small are antonyms.
And as far as D is concerned: all words should be defined in Thesaurus!
