Final answer:
A substance that is malleable and good at conducting electricity is a metal, as metals have these properties and are typically solid, shiny, and can be shaped into sheets or wires.
Step-by-step explanation:
If a substance is described as being very malleable and good at conducting electricity, the substance is likely a metal. Metals are elements that are characteristically solid at room temperature (with the exception of mercury), and they possess the ability to conduct heat and electricity effectively. They are also malleable, meaning they can be hammered into thin sheets, and ductile, meaning they can be drawn into thin wires without breaking. Furthermore, metals typically have a shiny appearance when cut or polished, known as luster. Therefore, the correct answer to the question is A. Metal.