Which of the following statements is true? Temperature is an average measure of the heat energy in a substance.
The transfer of heat in a fluid does not require physical contact between molecules.
The sun's energy comes from the nuclear reactions of changing hydrogen into helium.
All of the above.

Which best describes how fluids change as they travel through different portions of the convection currents? they change to solids at the outer portion of the convection currents. they change to solids at the inner portion of the convection currents. they become more dense at the outer portion of the convection currents. they become more dense at the inner portion of the convection currents