Which of the following theories states that diseases are caused by microorganisms?

The germ theory of disease is the foundation of modern microbiology and states that specific microorganisms, such as bacteria, viruses, and fungi, are the primary cause of many diseases. This theory emerged in the 19th century, revolutionizing our understanding of health and illness. By identifying the causal relationship between pathogens and disease, germ theory has led to significant advancements in public health, hygiene practices, and the development of vaccines and antibiotics.

In contrast to this concept, the environmental theory focuses on how external environmental factors affect health rather than attributing disease to specific microorganisms. The miasma theory posits that diseases were caused by "bad air" or noxious vapors, a belief that was debunked with the advancement of germ theory. Holistic theory, meanwhile, emphasizes the interconnectedness of body, mind, and environment in health, rather than blaming specific pathogens for diseases.

Thus, the germ theory is considered correct in identifying microorganisms as the causative agents of a variety of illnesses, forming a crucial framework in the study and practice of public health.