Concept:The word 'lucid' means clear and easy to understand. Its opposite is something unclear or not well-defined.
Explanation:Lucid refers to something that is clear, transparent, or logically expressed.
Vague directly means not clear, indefinite, or ambiguous.
Thus, vague is the correct antonym.
Transparent, clear, and coherent are all similar to lucid, not opposite.
Answer:Option C (Vague)