The correct options are
A Fossil fuels are difficult to extract.
B Burning of fossil fuels causes pollution.
C Burning of fossil fuels leads to greenhouse effect and global warming.
Fossil fuels are the major source of energy for generating electricity, industry usage, fuel in vehicles etc.
Burning of fossil fuel creates smoke and carbon dioxide. Smoke produced from the burning of fossil fuels is a major source of pollution and the carbon dioxide produced by burning the fossil fuels causes greenhouse effect which in turn contributes to global warming.
Fossil fuels are found deep under the earth. This has led to many accidents in mines which have costed many human lives.