Which choice defines ac and dc correctly?

in ac, electrons moving in one direction. in dc, they move in one direction and then in the other direction.

in dc, electrons move in only one direction. in ac, electrons move in one direction and then in the other direction.

in ac and dc, electrons move in the same direction.

in ac and dc, electrons move in opposite directions.

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