Read the following passage and mark the letter A, B, C, or D to indicate the correct word or phrase

There are many sources of energy. Some are renewable, but others may (1) ______ in the future. Fossil fuels like coal, oil, and gas are non-renewable and used to produce (2) ______. However, they cause pollution and contribute to climate change.
Energy (3) ______ essential for modern life, so we must find ways to use it efficiently. To protect the environment, we should use more (4) ______ such as wind and solar power. Solar panels can (5) ______ electricity from sunlight, while wind turbines convert wind into energy. These clean sources are sustainable and widely used in many countries. In some places, wind turbines are built (6) ______ open fields to generate power efficiently.