Option B ‘Transmittable’ is the most appropriate synonym of the word given in the sentence. Meaning of the other words are: Complicated means consisting of many interconnecting parts or elements; intricate. Transmittable means (of an emotion, feeling, or attitude) likely to spread to and affect others, catching. Effective means successful in producing a desired or intended result. Unthinkable means (of a situation or event) too unlikely or undesirable to be considered a possibility.