Answer:
wind, solar, bioproduction
Step-by-step explanation:
The wind energy, since in some places the wind reaches fast velocities, the scientist try to implement new technology to improve how to convert wind energy in electricity for example.
The solar energy, even we have by now the solar panels, there is still an area to research to obtain again the mayor quantity of energy with less materials.
The bioproduction, since the mammals we produce liquid and solid wastes, how to convert it into energy like gas, electricity, etc.