Correct Answer: B

Rationale: The correct answer is B: Mycobacterium tuberculosis. Acid-fast bacteria have a unique cell wall component called mycolic acid, making them resistant to decolorization by acid-alcohol during staining. Mycobacterium tuberculosis is acid-fast, as it retains the stain due to its high lipid content. Streptococcus pyogenes (A), Clostridium perfringens (C), and Bacillus subtilis (D) do not possess mycolic acid in their cell walls, so they are not acid-fast.

Correct Answer: B

Rationale: The correct answer is B: Sexual transmission. The symptoms described are indicative of a vaginal yeast infection caused by Candida albicans. The presence of large gram-positive oval oblong cells forming pseudomycelium is characteristic of Candida infection. Sexual transmission is the most probable channel of infection as Candida can be transmitted through sexual contact. Endogenous infection (A) refers to infections originating from the body's own flora, which is not the case here. Contact infection (C) typically involves direct physical contact or fomite transmission, which is less likely in this scenario. Vector-borne transmission (D) involves transmission through vectors like mosquitoes or ticks, which is not relevant in this case.

Correct Answer: C

Rationale: The correct answer is C because "Infectious disease" is a combination of both a clinical term (A) and a term expressing the possibility of developing certain symptoms in an infection (B). Infectious diseases are illnesses caused by pathogenic microorganisms, such as bacteria, viruses, parasites, or fungi, that can spread directly or indirectly from person to person. Therefore, the term encompasses both the clinical aspect of the disease and the potential symptoms that may manifest in an infected individual. Choices A and B alone do not fully capture the comprehensive definition of infectious disease, making C the correct answer. Choice D is incorrect as there is a correct answer in this case.

Correct Answer: B

Rationale: The correct answer is B: Carrying antibiotic resistance genes. Bacterial plasmids are small, circular DNA molecules that can carry genes, including those for antibiotic resistance. This allows bacteria to survive exposure to antibiotics. Plasmids do not directly regulate bacterial growth (A), produce toxins (C), or facilitate endospore formation (D). Plasmids play a crucial role in the spread of antibiotic resistance among bacteria.

Correct Answer: D

Rationale: The correct answer is D because all three bacteria (Neisseria meningitidis, Haemophilus influenzae, and Streptococcus pneumoniae) can cause bacterial meningitis. Neisseria meningitidis is a common cause of meningococcal meningitis, Haemophilus influenzae can cause H. influenzae meningitis, and Streptococcus pneumoniae is a leading cause of pneumococcal meningitis. Therefore, all of the above choices are correct. The other choices are incorrect because each of the bacteria listed can independently cause bacterial meningitis, so none of them alone can be the sole correct answer.