Which of the following statements is true? a. An insulator speeds up the transfer of heat.
b. Radiation is the transfer of heat in solids.
c. All moving objects experience friction.
d. All work gains some energy as heat.

C is correct

Explanation:

For example, you move your hands together you are creating friction.

gravity causes stares to cluster i think so

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.