During the expansion of the early universe, which two interactions were the last to separate? a. the strong and weak interactions b. the gravitational and strong interactions c. the electromagnetic and weak interactions or d. the electromagnetic and gravitational interactions

Which of the following best describes internal energy? a. the difference between the kinetic and potential energies of the particles in a system b. the sum of the kinetic and potential energies of the particles in a system c. the sum of the kinetic and thermal energies of the particles in a system d. the difference between the kinetic and thermal energies of the particles in a system