The key signal here is the word strange/puzzling at the start — this sets up a contrast. If her writing is commonly thought to be tortuous (meaning twisting, overly complex, hard to follow), then the blank must introduce a word that contradicts that reputation.

• Painstaking — means thorough and careful; does not contradict the notion of being tortuous.
• Tedious — means boring and slow; actually reinforces the idea of difficult writing.
• Insightful — means perceptive; does not directly contrast with being hard to follow.
• Clear — directly contradicts the notion of tortuous (convoluted) writing. If her essays are extremely clear, it is indeed strange that she has a reputation for complexity.

Correct Answer: D — Clear. The sentence uses “although” to signal contrast, and the framing word “strange” confirms we need the opposite of tortuous.