Answer:
The correct answers are: oil, coal and nuclear power.
Step-by-step explanation:
Coal and oil are two of the three types of fossil fuel energy. The problem that arises from producing energy from burning fossils is that too much carbon dioxide (a greenhouse gas) is liberated into the air, which contributes to global warming and other environmental issues.
Nuclear power is the use of nuclear and chemical reactions to produce energy (in nuclear power plants). The problem comes with the waste that is produced in this process, which has dangerous levels of radioactivity.
Hydroelectric power is an energy source that does not harm the environment as the above since it uses the power of water in motion to produce the energy. It is similar to geothermal (energy produced from beneath the earth) and solar power.