Explanation
In this vocabulary item, Rebellious is the closest synonym of Defiant, so option B is correct. The word Defiant and the word Rebellious share the same central sense in the context tested by the question, although usage, tone and grammatical form should still be checked before substituting one for the other. A synonym is not required to be identical in every possible sentence; it must preserve the intended meaning in the relevant context. Here, replacing Defiant with Rebellious keeps the core idea intact without reversing the tone or changing the action, quality or state expressed by the target word. The alternatives Frank, Jealous and Investigate do not express the same central meaning as Defiant. This distinction matters because competitive examinations often place one accurate synonym beside three familiar but contextually unsuitable words. To verify Defiant independently, identify its part of speech, state a short definition, and place both Defiant and Rebellious in the same simple sentence. If the sentence retains its essential meaning and grammatical structure, the synonym relationship is supported. Learners should revise Defiant together with Rebellious, a brief usage cue and the contrasting distractors.