The way people disposed of human waste in 19th-century London was dangerous because

filled the air with germs.

it made people nauseous.

it put night soil men out of business.

it polluted drinking water with deadly bacteria.

The correct answer is D. It polluted drinking water with deadly bacteria.

Explanation

During the mid-nineteenth century in London, an event known as the great stench occurred, caused by the dumping of sewage, human solid waste, factory waste, slaughterhouses, and others into the waters of the River Thames, which caused its contamination. At the same time, the waters of this river were used by the community of this city for cooking, bathing, and drinking. This caused a large number of people to acquire illnesses when consuming the water of this river, mainly the Cholera. According to the above, the correct answer is D. It polluted drinking water with deadly bacteria.