Arenewable energy source that relies on falling from a height levels to produce electricity is
wind power
nuclear power
hydroelectric power
geothermal power

Answer;

Hydroelectric power

Explanation;Hydroelectric power is produced when a turbine converts the kinetic energy of falling water into mechanical energy. Then a generator converts the mechanical energy from the turbine into electrical energy. Hydroelectric power plants uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity.

Gallium melts near room temperature and has one of the largest  liquid  ranges of any metal, so it has found use in high temperature thermometers.

What are the choices?