Correct Answer: B

Rationale: The correct answer is B. Immunity after a single tetanus vaccination is of limited duration, usually around 10 years. Booster vaccinations are needed to maintain protection due to waning immunity over time. Choice A is incorrect as immunity is not usually lifelong. Choice C is incorrect as tetanus toxoid is a sterile vaccine and does not cause infection. Choice D is also incorrect as there is a correct answer, which is B.

Correct Answer: A

Rationale: The correct answer is A: Trichomonas vaginalis. Trichomonas vaginalis is a protozoan parasite that causes trichomoniasis, a sexually transmitted infection characterized by inflammation of urogenital tracts. The description of big unicellular pyriform organisms with a sharp spike on the back end of their bodies, big nucleus, and undulating membrane matches the morphology of Trichomonas vaginalis. Trichomonas hominis and Trichomonas buccalis are different species that do not cause urogenital infections. Trypanosoma gambiense is a protozoan parasite causing African trypanosomiasis and does not match the described morphology or symptoms.

Correct Answer: A

Rationale: Ribosomes are the target for antibiotics as they interfere with protein synthesis in bacteria. Aminoglycosides, tetracyclines, macrolides, and lincosamides all target ribosomes by inhibiting protein synthesis at different stages. Beta-lactam antibiotics target cell wall synthesis, not ribosomes. Antifolate compounds, quinolones, and raspicin target DNA synthesis and replication, not ribosomes. Therefore, the correct answer is A as it includes antibiotics that specifically target ribosomes for inhibiting bacterial protein synthesis.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. 1. Gram-positive cocci in chains suggest streptococci. 2. Beta-hemolytic activity indicates Streptococcus pyogenes. 3. Streptococcus pyogenes is commonly associated with sore throat (pharyngitis) and fever. 4. Streptococcus pneumoniae (choice B) is alpha-hemolytic and mainly causes pneumonia. 5. Enterococcus faecalis (choice C) is not typically associated with sore throat. 6. Staphylococcus aureus (choice D) is not commonly beta-hemolytic and is not a typical cause of pharyngitis.

Correct Answer: C

Rationale: The correct answer is Shigella (Choice C) because it matches the description of being Gram-negative rods and lactose non-fermenters. Shigella is a non-lactose fermenting, Gram-negative rod that typically produces colorless colonies on Endo agar. Salmonella (Choice A) and Escherichia coli (Choice B) are both lactose fermenters and would produce pink colonies on Endo agar. Proteus (Choice D) is also a lactose fermenter and would appear pink on Endo agar. Therefore, based on the characteristics provided, Shigella is the most likely microorganism in this scenario.