Materials science and construction: Identify the correct combined statement about plastics and acoustical boards.

Introduction / Context:
Understanding the thermal and acoustic behavior of construction materials is essential for architectural and civil engineering decisions. Plastics, in particular, have distinct properties compared to metals like steel, and specialized products such as fiberglass–phenolic acoustical boards are used to control sound within buildings.

Given Data / Assumptions:

• Typical commodity plastics used in construction (for example, PVC, PE, PP, ABS) are being considered.
• Steel is the baseline reference for thermal expansion.
• Sound absorption coefficient values cited are representative textbook values for fiberglass–phenolic boards.

Concept / Approach:
We evaluate each statement on its own merits and then determine if all are simultaneously true. This is a conceptual verification task rather than a numerical one. The thermal expansion comparison is a rule-of-thumb used by engineers, and the acoustical coefficient cited aligns with mid-band absorption where fibrous boards perform strongly.

Step-by-Step Solution:
Check melting/softening: Many plastics soften or melt at relatively low temperatures compared to metals. Thus, “plastics have generally low melting point” is acceptable for broad design guidance.Thermal expansion: Typical linear thermal expansion for plastics is several times that of steel (steel ~12 x 10^-6 per °C; many plastics ~40–150 x 10^-6 per °C). A factor of about three (or more) is a fair engineering approximation.Acoustical boards: Fiberglass mats impregnated with phenolic resin can exhibit high mid-frequency absorption. A value around 0.67 is plausible depending on thickness and mounting.Since each independent statement is valid, the combined answer is “All of the above.”

Verification / Alternative check:
Compare standard data sheets for plastics’ thermal expansion, and catalog data for fiberglass/phenolic acoustical panels to confirm typical absorption coefficients in the 0.6–0.8 range at mid frequencies.

Why Other Options Are Wrong:
Options A–C alone are incomplete; the comprehensive truth is captured by D.“None of the above” is clearly false because each individual statement is supportable.

Common Pitfalls:
Confusing glass transition with melting in amorphous plastics; for design, both represent low thermal limits versus metals.

Final Answer:
All of the above.