Correct Answer: A

Rationale: The correct answer is A: IgG. IgG is the most abundant class of immunoglobulins in the body, constituting about 75% of total immunoglobulins. IgG plays a crucial role in long-term immunity, neutralizing toxins, and enhancing phagocytosis. IgE is involved in allergic reactions, IgD is mainly found on B cells and functions as a receptor, and IgM is the first antibody produced in response to an infection but is less abundant compared to IgG. Therefore, IgG is the correct choice based on its abundance and diverse functions in the immune system.

Correct Answer: C

Rationale: Rationale: 1. Presence of gram-negative bacilli suggests Enterobacteriaceae family, which includes E. coli. 2. Green soluble pigment indicates pyocyanin production, characteristic of E. coli. 3. E. coli is the most common cause of acute cystitis due to its ability to colonize the urinary tract. Summary: A: Pseudomonas aeruginosa is not typically associated with acute cystitis and does not produce mucous colonies. B: Klebsiella pneumoniae may cause UTIs, but does not produce green pigment and is less common than E. coli. D: Salmonella enteritidis is associated with gastrointestinal infections, not cystitis.

Correct Answer: D

Rationale: The correct answer is D because the catarrhal stage of whooping cough is characterized by mild respiratory symptoms such as mild coughing, sneezing, or a runny nose. During this stage, the cough may start to worsen but is not yet severe. A: Incorrect - Decrease in paroxysms of coughing is not seen in the catarrhal stage; it occurs later in the paroxysmal stage. B: Incorrect - Subsequent respiratory infection for many months after the onset of pertussis is not a characteristic of the catarrhal stage. C: Incorrect - Uncontrollable coughing followed by a high pitched 'whoop' sound is typical of the paroxysmal stage, not the catarrhal stage.

Correct Answer: A

Rationale: The correct answer is A: mRNA. mRNA carries the genetic code from the DNA in the cell nucleus to the ribosomes in the cytoplasm, where protein synthesis occurs. It serves as a template for protein synthesis by specifying the order of amino acids. tRNA (choice B) brings amino acids to the ribosome during protein synthesis. rRNA (choice C) is a structural component of ribosomes. snRNA (choice D) is involved in RNA processing and splicing, not protein synthesis. Therefore, choice A is correct as it directly carries the genetic code for protein synthesis.

Correct Answer: B

Rationale: The correct answer is B: Herpangina. Family Parvoviridae includes Parvovirus B19, which causes Fifth disease, aplastic crisis in chronic anemia, and fetal infections. Herpangina is caused by Enteroviruses, not Parvoviridae. Parvovirus B19 specifically targets erythroid progenitor cells, leading to anemia in susceptible individuals. Fetal infections can result in hydrops fetalis. Aplastic crisis occurs in patients with chronic anemia due to suppression of erythropoiesis by the virus.