Lens accommodation rate indicates approach speed

Steps:

• The eye's lens thickens (more convex) as the bird approaches, reducing focal length for closer focus.
• Graph plots lens shape (curvature) over time; steeper slope means faster curvature change.
• Fastest approach occurs where distance decreases quickest, causing maximum rate of lens adjustment.
• Identify point with steepest negative slope in curvature-time graph.

Why C is correct:

• At C, the lens curvature changes most rapidly, matching the definition of accommodation rate proportional to radial approach velocity.

Why the others are wrong:

• A: Gradual slope indicates slower approach.
• B: Moderate slope shows intermediate speed.
• D: Flattening slope means slowing or receding.

Final answer: C