The correct answer is: A. Burning coal.
Mercury is a naturally occurring element that can be found in the Earth’s crust, water, and air. It is also used in a variety of products, including batteries, thermometers, and fluorescent lights. When mercury is burned, it releases mercury vapor into the air. This vapor can be inhaled and can cause a variety of health problems, including neurological damage, kidney damage, and reproductive problems.
Burning garbage can also release mercury into the air, but this is not as common as burning coal. Coal is a major source of mercury emissions in the United States. In 2017, coal-fired power plants were responsible for 43% of all mercury emissions in the United States.
Steam engines do not emit mercury into the air. Steam engines use heat to convert water into steam, which then drives a turbine. The turbine generates electricity. There is no mercury involved in this process.
In conclusion, the correct answer is: A. Burning coal.