Correct Answer: A

Rationale: The correct answer is A: Streptococcus pneumoniae. This bacterium is the most likely causative agent because it is a Gram-positive cocci in pairs with a capsule, which matches the description provided. S. pneumoniae is a common cause of bacterial pharyngitis and can present with sore throat.

Summary of other choices:
B: Staphylococcus aureus is a Gram-positive cocci in clusters, not pairs, and is not typically associated with sore throat.
C: Neisseria meningitidis is a Gram-negative diplococcus and more commonly causes meningitis or septicemia, not sore throat.
D: Klebsiella pneumoniae is a Gram-negative rod bacterium, not a Gram-positive cocci, and is not a common cause of sore throat.

Correct Answer: A

Rationale:
Step-by-step rationale for why Answer A (Sabouraud's) is correct:
1. Sabouraud's agar is a selective medium for fungi.
2. Candida is a type of fungus causing candidosis.
3. Sabouraud's agar promotes fungal growth.
4. Candida will grow on Sabouraud's agar, confirming the diagnosis.
5. Other choices are for bacterial culture, not suitable for fungal growth.
Summary:
- Endo, Jensen's, and Roux are not appropriate for fungal culture.
- Sabouraud's agar specifically supports fungal growth, making it the correct choice for confirming candidosis.

Correct Answer: D

Rationale: The correct answer is D: Yersinia enterocolitica. This bacterium can contaminate foods and grow at refrigerator temperatures due to its psychrotrophic nature. Yersinia enterocolitica is known to cause foodborne illnesses even when stored at cold temperatures. Shigella sonnei is a human pathogen transmitted through fecal-oral route, Campylobacter jejuni is typically found in poultry and causes food poisoning, and E. coli can cause foodborne illnesses but does not grow well at refrigerator temperatures.

Correct Answer: A

Rationale:
Rationale:
1. Endo agar inhibits the growth of Gram-positive bacteria.
2. Colorless colonies on Endo agar indicate lactose non-fermenting bacteria.
3. Shigella dysenteriae is a lactose non-fermenting, Gram-negative rod, causing dysentery.
4. Salmonella typhi, Escherichia coli, and Proteus vulgaris are lactose fermenters, so they would produce pink colonies on Endo agar.

Therefore, the most likely causative agent is Shigella dysenteriae.

Correct Answer: C

Rationale: The correct answer is C: ECHO virus infection. ECHO virus is transmitted via the fecal-oral route, meaning the virus is passed from feces to the mouth. This transmission occurs through contaminated food, water, or surfaces. Relapsed fever and spotted fever are generally transmitted by arthropod vectors like ticks. Pertussis, also known as whooping cough, spreads through respiratory droplets.
Therefore, the fecal-oral route is not applicable to these diseases.