If a polymer softens and melts when you heat it, it is called a/an

thermoset plastic

thermoplastic

elastomer

electromagnetic waves travel through space with vacuums. give me brainliest if right.

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.