Writing has long been a primary tool for thinking.______________________________________________________________. The articulation of thought, a foundational human skill, risks atrophy due to the deployment of AI. ‘Help’ from AI is a gentle, persistent pressure removing idiosyncrasies and pushing writers towards a standardised, middle-of-the-road voice. In a manner of speaking, the originality of the writer’s voice is lost. Hence, the unique signature of the writer is eroded by an algorithm.

The opening line claims writing is a primary tool for thinking. The following lines say AI deployment causes "atrophy" of articulation and erodes the writer's unique signature. The missing sentence must connect the two.

Why Option 3 (correct): "When that process is delegated to an outside agency, thinking itself becomes superficial" provides the bridge — if writing is the tool *for* thinking, outsourcing the writing means outsourcing the thinking, hence superficiality and atrophy.

Why other options fail:

• Option 1 & Option 4: praise AI's role in clarifying thought or producing smooth prose — contradicts the passage's critical view.
• Option 2: about *communicating* difficult concepts; the passage is about *thinking*, not transmission.