Answer:
The correct option is : D. Bad air
Explanation:
The germ theory is one of the widely accepted scientific theories. It states that diseases can be caused due to some microorganisms. These microorganisms are called germs or pathogens.
Before the germ theory, the miasma theory was predominant. According to the miasma theory, diseases like chlamydia and cholera, were caused by a miasma or bad air. The bad air was defined as a foul smelling poisonous air produced by decomposition of matter.
