Purely elastic behavior means reversible deformation up to the elastic limit

Steps:

• Recall that purely elastic materials return to original shape after stress removal, following Hooke's law (stress ∝ strain).
• Identify materials: Assume A is plastic (permanent deformation), B is rubber or steel below yield point (fully reversible), C is viscoelastic (time-dependent), D is brittle (fractures without plasticity).
• Compare behaviors: Eliminate options showing plastic, viscous, or failure modes.
• Select the one with no permanent strain after unloading.

Why B is correct:

• B follows Hooke's law perfectly, with zero residual strain, defining ideal elasticity.

Why the others are wrong:

• A shows plastic deformation, leaving permanent change.
• C involves viscous flow, not purely elastic.
• D fractures elastically but not reusable without damage.

Not enough information on specific materials, but based on standard examples, B fits.

Final answer: B