A sensitized B cell is activated once:

Correct Answer: A

Rationale: The correct answer is A because a sensitized B cell requires activation by a helper T cell releasing cytokines to undergo differentiation and proliferation into plasma cells. This interaction is crucial for initiating the humoral immune response. Choices B, C, and D are incorrect because binding to a cytotoxic T cell, cloning of memory B cells, or cloning of plasma cells do not directly activate a sensitized B cell for its function in producing antibodies.

Correct Answer: C

Rationale: The correct answer is C: electrolyte balance. Hemoglobin's affinity for oxygen is primarily influenced by factors such as pH, temperature, and the partial pressure of oxygen (PO2). Electrolyte balance, on the other hand, does not directly impact hemoglobin's ability to bind with oxygen. Changes in electrolyte levels may affect overall blood composition but do not directly alter hemoglobin's oxygen-binding capacity. Therefore, electrolyte balance does not affect hemoglobin's affinity for oxygen, making it the correct choice. RBC metabolic activity can impact oxygen release from hemoglobin, temperature can affect hemoglobin's oxygen-binding capacity, and the PO2 of blood directly influences oxygen binding to hemoglobin.

Correct Answer: C

Rationale: Emphysema is the correct answer because it is characterized by the destruction of alveolar walls and connective tissues in the lungs, leading to reduced respiratory surface area. Asthma is characterized by airway inflammation and bronchoconstriction. Bronchitis is inflammation of the bronchial tubes. Tuberculosis is a bacterial infection affecting the lungs. Emphysema best fits the description provided in the question.

Correct Answer: C

Rationale: The correct answer is C: Smoking. Smoking is a risk factor for developing heart failure because it damages the blood vessels, increases blood pressure, and reduces oxygen delivery to the heart. Regular exercise (A) is actually beneficial for heart health. Low blood cholesterol levels (B) are generally considered a positive factor for heart health. Adequate sleep (D) is important for overall well-being but is not a direct risk factor for heart failure. In conclusion, smoking (C) stands out as the correct answer due to its harmful effects on the cardiovascular system.

Correct Answer: C

Rationale: The larynx consists of 9 cartilages, including the thyroid, cricoid, and epiglottis. These structures provide support and protection to the vocal cords and are essential for phonation and breathing. Choice C is correct because it accurately reflects the number of cartilages in the larynx. Choices A, B, and D are incorrect as they do not correspond to the anatomical structure of the larynx. It is important to understand the specific components of the larynx to correctly identify the number of cartilages present.