Not all the time or 100% of time .
According to the official SE question, which are those count and nothing else, USUALLY in SE question you do have two pairs of choices that are synonyms and two other words out of scope, for a grand total of 6 answer choices.
However, this does not happen ALL the time . Moreover, the ETS GRE instructions tell us that the two words to fit in the blank must be ALIKE in meaning.
I.E they must give the same meaning to the sentence as a whole. There are cases in which you do have tow words which are NOt synonyms that give to the sentence the same meaning. The vast majority are synonyms BUT not all the time.
BTW, this is NOT an offoicia question for that count
Hope this helps
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