Correct Answer: A

Rationale: The correct answer is A: Helicobacter pylori. This bacterium is a major cause of gastric ulcers by disrupting the balance between aggressive (acid, pepsin) and defensive (mucus, bicarbonate, prostaglandins) factors in the stomach lining. H. pylori infection leads to inflammation, weakening the protective mucosal barrier, making the stomach more susceptible to damage. Choices B, C, and D are defensive factors that help protect the stomach lining and prevent ulcer formation, so they do not contribute to the development of gastric ulcers.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. The given characteristics match this bacterium: Gram-positive diplococci, catalase-negative, and alpha-hemolytic. S. pneumoniae is a common cause of community-acquired pneumonia. Other choices are incorrect because Staphylococcus aureus is catalase-positive, Enterococcus faecalis is not alpha-hemolytic, and Klebsiella pneumoniae is not Gram-positive diplococci.

Correct Answer: B

Rationale: The correct answer is B: kidneys. The kidneys are the primary organs responsible for excreting drugs from the body through urine. They filter the blood and remove waste products, including drugs, through the process of urine formation. The lungs primarily excrete gases and volatile substances, not drugs. The small intestines are mainly involved in absorption of nutrients, not drug excretion. The spleen is part of the immune system and does not play a direct role in drug excretion.

Correct Answer: D

Rationale: The correct answer is D: Single stranded segmented (-) RNA. Orthomyxoviridae family includes influenza viruses, which have a genome composed of single-stranded segmented negative-sense RNA. This specific structure allows for efficient replication and transcription within host cells. Choice A is incorrect as orthomyxoviruses do not have a double-stranded DNA genome. Choice B is incorrect because orthomyxoviruses have a negative-sense RNA genome, not a positive-sense RNA genome. Choice C is incorrect as orthomyxoviruses do not have a double-stranded RNA genome.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Anopheles mosquitoes are the primary vectors for transmitting malaria. 2. They prefer stagnant water for breeding, common in tropical regions. 3. Culex mosquitoes primarily spread diseases like West Nile virus. 4. Aedes mosquitoes transmit diseases like Zika and dengue fever. 5. Mansonia mosquitoes are known for transmitting filarial diseases. Therefore, the correct answer is A (Anopheles), as they are specifically associated with spreading malaria.