Correct Answer: A

Rationale: The correct answer is A (20 min) because Escherichia coli typically has a generation time of around 20 minutes, meaning the time it takes for a bacterial population to double. This rapid reproduction rate is a key characteristic of E. coli. Option B (60 min) is incorrect as it is longer than the usual generation time. Option C (20 hours) is too long for E. coli's generation time. Option D (24 hours) is also incorrect as it is much longer than the typical generation time of E. coli.

Correct Answer: A

Rationale: The correct answer is A: Bacterial endospores. Bacterial endospores have a higher resistance to environmental stresses due to their unique structure, which includes a tough outer layer that protects the spore from harsh conditions such as heat, chemicals, and radiation. This protective layer allows endospores to remain dormant and survive in unfavorable environments until conditions improve. Summary: B: Fungal spores - While fungal spores can also survive in harsh conditions, they are generally not as resistant as bacterial endospores due to differences in their protective structures. C: Enveloped viruses - Enveloped viruses are susceptible to environmental stresses as their lipid envelope can easily be damaged by heat, chemicals, and other factors. D: Vegetative bacterial cells - Vegetative bacterial cells are more susceptible to environmental stresses compared to endospores, as they do not have the same level of protective mechanisms to survive in unfavorable conditions.

Correct Answer: D

Rationale: The correct answer is D because Cytomegalovirus infections are caused by human herpesvirus 5, also known as Human Herpesvirus 5 (HHV-5) or Cytomegalovirus (CMV). This virus belongs to the Herpesviridae family, genus Betaherpesvirinae. Options A, B, and C are incorrect as they do not correspond to the specific virus responsible for causing Cytomegalovirus infections.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Hepatitis B infection can present with jaundice due to liver inflammation, elevated serum aminotransferase levels due to liver damage, and sometimes no symptoms in the acute phase. This comprehensive presentation covers the spectrum of possible clinical manifestations of hepatitis B infection. Choices A and B are correct as they are common manifestations of hepatitis B infection. Choice C is incorrect as hepatitis B infection can indeed present with symptoms, making option D the most appropriate choice.

Correct Answer: A

Rationale: The correct answer is A: Borrelia burgdorferi. This bacterium is known for causing Lyme disease, which is transmitted through tick bites. Borrelia burgdorferi is specifically associated with Lyme disease due to its ability to infect and spread within the body, leading to a range of symptoms if left untreated. Summary of incorrect choices: B: Clostridium difficile - Known for causing gastrointestinal infections, not Lyme disease. C: Streptococcus pneumoniae - Commonly causes pneumonia and other respiratory infections, not Lyme disease. D: Mycobacterium tuberculosis - Causes tuberculosis, a respiratory disease, not Lyme disease.