Pick up the correct statement from the following: A. Plastics have generally low melting point B. The coefficient of thermal expansion of plastics is about three times than that of steel C. The acoustical boards prepared by impregnating fibre-glass with phenolic resins has absorption coefficient of about 0.67 D. All the above

The correct answer is D. All the above.

Plastics have generally low melting points. This means that they can be easily melted and molded into different shapes. The coefficient of thermal expansion of plastics is about three times than that of steel. This means that plastics expand more than steel when heated. The acoustical boards prepared by impregnating fibre-glass with phenolic resins has absorption coefficient of about 0.67. This means that these boards are good at absorbing sound.

Here are some additional details about each option:

• Option A: Plastics have generally low melting points. This is because plastics are made up of long chains of molecules that are held together by weak bonds. When these bonds are broken, the plastic melts. The melting point of a plastic can vary depending on the type of plastic and the additives that are used.
• Option B: The coefficient of thermal expansion of plastics is about three times than that of steel. This means that plastics expand more than steel when heated. The coefficient of thermal expansion is a measure of how much a material expands or contracts when its temperature changes. The coefficient of thermal expansion of plastics is typically higher than that of metals because plastics are made up of long chains of molecules that can move more easily than the atoms in metals.
• Option C: The acoustical boards prepared by impregnating fibre-glass with phenolic resins has absorption coefficient of about 0.67. This means that these boards are good at absorbing sound. The absorption coefficient of a material is a measure of how much sound it absorbs. The absorption coefficient of a material can vary depending on the type of material, the thickness of the material, and the frequency of the sound.