Answer: c) Nonmetals
Explanation: Nonmetals are generally poor conductors of heat and electricity due to their lack of free electrons. Metallic bonding, which is prevalent in metals and alkaline earth metals, allows for better conductivity because electrons can move freely. Metalloids can exhibit properties of both metals and nonmetals, but they are often more conductive than nonmetals. Therefore, among the options provided, nonmetals are the materials that typically show poor conductivity.