2. Which extraction method is commonly used for coal? a. Thermal cracking b. Hydraulic fracturing c. Surface mining d. Geothermal drilling

The correct answer is c. Surface mining.<br /><br />Surface mining is the most commonly used extraction method for coal. It involves removing the soil and rock above the coal seam and then extracting the coal. This method is typically used when the coal deposit is close to the surface. Other methods like thermal cracking, hydraulic fracturing, and geothermal drilling are not commonly used for coal extraction.