Steepest slope indicates stiffest fiber

Steps:

• Identify the extension-load graph where y-axis is extension and x-axis is load.
• The slope of each curve equals extension per unit load; steeper slope means more extension (easier stretch).
• Compare slopes across A, B, C, D over the load range.
• Select the curve with the shallowest slope, showing least extension for given load.

Why D is correct:

• D has the shallowest slope, indicating highest stiffness (k = load/extension from Hooke's law), so most difficult to stretch.

Why the others are wrong:

• A: Steeper slope than D, easier stretch.
• B: Moderate slope, less stiff than D.
• C: Steepest slope, easiest stretch.

Final answer: D