Correct Answer: D

Rationale: The correct answer is D: Metabolic acidosis. Severe diarrhea can lead to metabolic acidosis because the loss of bicarbonate ions in the stool results in an overall decrease in the body's bicarbonate levels. Respiratory acidosis (choice A) is caused by retention of carbon dioxide, usually due to inadequate alveolar ventilation. Metabolic alkalosis (choice B) is characterized by elevated pH and bicarbonate levels, usually caused by conditions like vomiting. Respiratory alkalosis (choice C) is a condition of low blood carbon dioxide levels and high pH, often due to hyperventilation.

Correct Answer: A

Rationale: The correct answer is A. The kidneys are crucial in maintaining acid-base balance by removing hydrogen ions to decrease acidity and retaining bicarbonate ions to increase alkalinity. Choice B is incorrect because the conversion of ammonia into urea is related to nitrogen waste excretion, not acid-base balance. Choice C is incorrect as aldosterone regulates sodium levels, not acid-base balance. Choice D is also incorrect as renin is involved in regulating blood pressure, not acid-base balance.

Correct Answer: B

Rationale: The correct answer is B: 'Use of nitrates.' Tadalafil (Cialis) is contraindicated in patients taking nitrates due to the risk of severe hypotension. Nitrates and Cialis both cause vasodilation, which can lead to a dangerous drop in blood pressure when used together. Choices A, C, and D are incorrect because a history of hypertension, use of antihypertensive medications, and a history of peptic ulcer disease are not specific contraindications for tadalafil use.

Correct Answer: D

Rationale: The correct answer is D: Use of nitrates. Sildenafil (Viagra) is contraindicated in patients taking nitrates due to the risk of severe hypotension. Nitrates and sildenafil both cause vasodilation, and the combination can lead to a dangerous drop in blood pressure. Choice A, peptic ulcer disease, is not a contraindication for sildenafil use. Choice B, a history of myocardial infarction, is not a contraindication unless the patient is also taking nitrates. Choice C, recent use of antihypertensive medications, is not a contraindication but requires caution as the combination can lead to additive effects lowering blood pressure.

Correct Answer: B

Rationale: Shivering is a physiological response to fever, as the body attempts to generate heat to increase the internal temperature. Hyperthermia, on the other hand, does not involve shivering. Absence of sweating (choice A) is more indicative of hyperthermia, as the body struggles to cool down without sweating. Lack of thirst (choice C) can be seen in both fever and hyperthermia. Increased heart rate (choice D) can occur in both fever and hyperthermia due to the body's attempt to regulate temperature.