Concept:A synonym is a word that has the same or nearly the same meaning as another word. ‘Plausible’ describes something that seems reasonable, likely, or credible.Explanation:Plausible means appearing true or believable. The correct synonym is ‘Believable’. Option A: ‘Unlikely’ means not probable, opposite to plausible. Option B: ‘Unbelievable’ means hard to accept as true. Option D: ‘Incredible’ means extremely difficult to believe. Only ‘Believable’ matches the meaning of plausible.Answer:C. Believable