The most important practice in preventing the spread of disease is:

Correct Answer: B

Rationale: The correct answer is B: Proper handwashing. This is the most important practice in preventing the spread of disease because it effectively removes germs and bacteria from hands, reducing the risk of transmission. Handwashing is crucial in healthcare settings to prevent infections. A: Wearing masks during patient contact is important, but handwashing is more effective in preventing disease spread as it directly addresses the transmission of germs through hands. C: Wearing disposable lab coats is important for infection control but not as crucial as proper handwashing, which directly removes germs from hands. D: Identifying specimens with red labels is important for handling potentially infectious materials, but handwashing is still the most essential practice in preventing disease spread as it addresses the primary mode of transmission through hands.

Correct Answer: A

Rationale: The correct answer is A: IgE antibody. IgE antibodies are involved in Type I hypersensitivity reactions, such as anaphylaxis caused by bee stings. IgE antibodies bind to mast cells and basophils, triggering the release of inflammatory mediators like histamine, causing respiratory distress and unconsciousness. IgG antibodies (choice B) are not typically involved in immediate hypersensitivity reactions. Sensitized T cells (choice C) are involved in delayed hypersensitivity reactions, not immediate ones like anaphylaxis. Complement (choice D) is part of the innate immune system and is not directly involved in IgE-mediated allergic reactions like anaphylaxis.

Correct Answer: B

Rationale: The correct answer is B because tumor-associated transplantation antigens can vary between different tumors of different histologic types even if induced by the same carcinogen. This is due to the fact that different histologic types of tumors can express different antigens, leading to variations in the transplantation antigens. Choice A is incorrect because tumor-associated transplantation antigens can differ even with the same carcinogen. Choice C is incorrect because the strength of the antigens is not specified in the question. Choice D is incorrect as tumor-associated transplantation antigens can indeed induce an immune response.

Correct Answer: D

Rationale: The correct answer is D because natural killer cells are a type of innate immune cell that can recognize and kill virus-infected cells without the need for prior sensitization. They are part of the body's first line of defense against viral infections. Choice A is incorrect because B cells are a type of adaptive immune cell involved in antibody production, not natural killer cells. Choice B is incorrect because cytotoxic T cells are also adaptive immune cells that require prior sensitization to target specific antigens. Choice C is incorrect because immunization typically boosts adaptive immune responses involving B and T cells, not natural killer cells.

Correct Answer: D

Rationale: The correct answer is D because in the determination of serum insulin levels by radioimmunoassay, we need isotope-labeled insulin (choice A) as a tracer for detection, anti-insulin antibody made in goats (choice B) to bind to insulin, and anti-goat gamma globulin made in rabbits (choice C) to detect the antibody bound to insulin. Isotope-labeled anti-insulin antibody made in goats (choice D) is not needed as it is not typically used in this assay. This choice would not contribute to the accurate measurement of serum insulin levels.