(c) Solar energy because we just have to use solar panels.
In the case of nuclear energy the elements such as plutonium and uranium are highly radioactive in nature and are expensive in finding out. Any leak or damage in the nuclear power plant can cause many diseases and many environmental problems. In the case of thermal energy coal is used and coal is a fossil fuel. A lot of air pollution is caused due to the burning of coal. In the case of geothermal energy the energy is absorbed by the pressure by the heat from the core which can sometimes be extremely hot and dangerous