Stiffness from load-stretch graph slope

Steps:

• Identify the load-stretch graph where x-axis is stretch and y-axis is load.
• Determine slope of each fiber's curve, as slope equals stiffness (load per unit stretch).
• Compare slopes: higher slope means less stretch for same load, thus more difficult to stretch.
• Select fiber with steepest slope over given load range.

Why D is correct:

• D has the highest slope, indicating greatest stiffness per Hooke's law (stress/strain), so resists stretch most.

Why the others are wrong:

• A: Lowest slope shows easiest stretch due to high compliance.
• B: Moderate slope allows more stretch than D.
• C: Higher slope than A/B but lower than D, so stretches more easily.

Final answer: D