Correct Answer: A

Rationale: The correct answer is A: protozoans. Pinworms are commonly referred to as Enterobius vermicularis, which are parasitic worms belonging to the phylum Nematoda. Protozoans are single-celled organisms, and pinworms are multicellular worms. Algae are photosynthetic organisms, helminths are parasitic worms (which pinworms fall under), and fungi are eukaryotic organisms that include molds and yeasts. Therefore, protozoans are the correct choice for organisms commonly referred to as pinworms.

Correct Answer: B

Rationale: Step-by-step rationale for why choice B (Tuberculin is introduced) is correct: 1. Tuberculin test helps identify individuals with latent TB infection. 2. Negative skin-allergic samples suggest absence of active TB. 3. Introducing tuberculin can help confirm latent TB infection. 4. Antibiotics are not prescribed for negative skin-allergic samples. 5. Vaccines are not administered for TB diagnosis. Summary: - Choice A is incorrect as antibiotics are not prescribed for negative skin-allergic samples. - Choice C is incorrect as vaccines are not used for TB diagnosis. - Choice D is incorrect as introducing tuberculin is the appropriate step in this scenario.

Correct Answer: D

Rationale: Step 1: Formic acid is produced during fermentation by Actinomyces. Step 2: Actinomyces are known to produce organic acids like formic acid through fermentation. Step 3: Other choices like Streptococcus, Klebsiella, and Clostridium are not typically associated with formic acid production. Step 4: Actinomyces is the most likely candidate based on its fermentation capabilities. Summary: Actinomyces is the correct answer because it is known to produce formic acid during fermentation, while the other choices lack this specific metabolic function.

Correct Answer: C

Rationale: The correct answer is C: cytoplasmic membrane. The cytoplasmic membrane is the fluidlike portion of a cell that separates the cell's contents from the external environment. It regulates the passage of substances in and out of the cell, maintains cell shape, and provides protection. Rationale: 1. Cytosol (choice A) is the liquid component of the cytoplasm where organelles are suspended, not the fluidlike portion of the cell. 2. Nucleoplasm (choice B) refers to the liquid component of the nucleus, not the entire cell. 3. Inclusion (choice D) refers to non-living substances within the cell that are not considered the fluidlike portion. Summary: The cytoplasmic membrane is the correct answer as it encompasses the entire cell and is responsible for maintaining cell integrity and regulating transport. Choices A, B, and D are incorrect as they do not represent the fluidlike portion of the cell.

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.