Correct Answer:
B. Lucid
This question assesses vocabulary, specifically choosing a word that implies clarity and ease of understanding.
- Foundational Fact: The sentence states that "everyone understood immediately," which indicates the explanation was very clear and easy to grasp.
- Correct Answer (B): "His explanation was so lucid that everyone understood immediately." The word "lucid" means expressed clearly; easy to understand. This perfectly aligns with the outcome of immediate comprehension.
- Why Distractors are Wrong:
- (A) "Obscure" means not discovered or known about; uncertain. An obscure explanation would be difficult to understand, contradicting the sentence.
- (C) "Ambiguous" means open to more than one interpretation; having a double meaning. An ambiguous explanation would cause confusion, not immediate understanding.
- (D) "Vague" means of uncertain, indefinite, or unclear character or meaning. A vague explanation would prevent immediate understanding, making it an unsuitable choice.