Correct Answer: B

Rationale: The correct answer is B: Thermophiles. Thermophiles are bacteria that can survive in extreme temperatures, typically between 45°C to 80°C. This ability is due to their unique enzymes and cell membrane structures that are adapted to high temperatures. Escherichia coli (A) is a common bacterium found in the human gut and does not thrive in extreme temperatures. Clostridium tetani (C) is a bacterium that causes tetanus and prefers moderate temperatures. Salmonella enterica (D) is a pathogenic bacterium that does not thrive in extreme temperatures. Therefore, Thermophiles are the only bacteria on the list known for surviving in extreme temperatures.

Correct Answer: A

Rationale: The correct answer is A: Centers for Disease Control and Prevention. The CDC is a U.S. government agency responsible for protecting public health and safety. The correct answer is the only choice that accurately reflects the agency's purpose. Choice B (Children's Disease Center) is incorrect because the CDC's scope is not limited to children's health. Choice C (Central Disaster Control Center) is incorrect as the CDC primarily focuses on disease prevention. Choice D (Central Drug Evaluation and Control Center) is incorrect as the CDC's main focus is not on drug evaluation. Thus, the correct answer is A as it aligns with the CDC's mission and responsibilities.

Correct Answer: A

Rationale: Rationale: 1. Dysenteric amoeba (Choice A) is the correct answer because it can exist asymptomatically in carriers and be transmitted through cysts. 2. Malarial plasmodium (Choice B) causes malaria, not carried asymptomatically in cysts. 3. Intestinal trichomonad (Choice C) causes trichomoniasis, not carried asymptomatically in cysts. 4. Dermatotropic leishmania (Choice D) causes skin lesions, not carried asymptomatically in cysts.

Correct Answer: C

Rationale: The correct answer is C: ensure survival under harsh conditions. Bacterial endospores are dormant, resistant structures that form under adverse conditions to protect the bacterial DNA and allow the bacterium to survive extreme environments. This function is crucial for the bacterium's long-term survival. Choice A is incorrect as endospores do not directly produce exotoxins. Choice B is incorrect as endospores do not store nutrients but rather protect the bacterium's genetic material. Choice D is incorrect as endospores do not enhance motility but rather enable survival during unfavorable conditions.

Correct Answer: D

Rationale: The correct answer is D because all of these symptoms are early signs of rabies. A short period of depression, nausea, and restlessness are common initial symptoms of rabies infection. These symptoms may be followed by more severe manifestations, such as aggression, confusion, and difficulty swallowing. Therefore, option D is the correct choice as it encompasses all the early symptoms of rabies. Options A, B, and C are incorrect as they focus on individual symptoms, whereas rabies typically presents with a combination of these early signs.