Correct Answer: A

Rationale: The correct answer is A: Plasmodium falciparum. Plasmodium falciparum is the most likely causative agent because the patient's symptoms of fever, chills, headache, and myalgia, along with the presence of intraerythrocytic ring forms and trophozoites on blood smear, are characteristic of malaria, particularly caused by P. falciparum in sub-Saharan Africa. Summary of other choices: B: Trypanosoma cruzi causes Chagas disease, which presents with symptoms like fever, rash, and swelling at the site of entry, not consistent with the patient's presentation. C: Borrelia burgdorferi causes Lyme disease, which typically presents with a characteristic rash (erythema migrans) and arthritis, not matching the patient's symptoms. D: Leishmania donovani causes visceral leishmaniasis, which presents with symptoms like weight loss, hepatosplen

Correct Answer: B

Rationale: The correct answer is B: Acute myocardial infarction (MI) is the most common cause of cardiogenic shock. During an MI, there is significant damage to the heart muscle, leading to a decrease in cardiac output and subsequent shock. This results in inadequate tissue perfusion and oxygen delivery. Choices A, C, and D are incorrect because decreased hemoglobin level (A) may lead to anemia but is not the most common cause of cardiogenic shock. Hypotension (C) is a symptom of shock, not the cause. Coronary artery disease (D) is a risk factor for MI but not the direct cause of cardiogenic shock.

Correct Answer: A

Rationale: The correct answer is A: Central retinal artery occlusion. This condition presents with sudden-onset, painless vision loss, cherry-red spot at the macula due to lack of blood flow, and attenuated retinal vessels. The cherry-red spot is due to the transparency of the fovea when there is ischemia in the surrounding retina. Central retinal vein occlusion (B) presents with sudden vision loss accompanied by retinal hemorrhages and dilated tortuous veins. Retinal detachment (C) typically presents with sudden flashes, floaters, and a curtain-like visual field defect. Acute angle-closure glaucoma (D) presents with severe eye pain, blurred vision, halos around lights, and a fixed mid-dilated pupil.

Correct Answer: A

Rationale: The correct answer is A: Ceftriaxone and azithromycin. Ceftriaxone covers Streptococcus pneumoniae, the most common pathogen in CAP, while azithromycin covers atypical pathogens like Mycoplasma pneumoniae. Vancomycin and piperacillin/tazobactam (choice B) are not first-line treatments for CAP. Ampicillin-sulbactam and levofloxacin (choice C) cover some pathogens but not as comprehensively as ceftriaxone and azithromycin. Clindamycin and cefepime (choice D) do not provide adequate coverage for typical CAP pathogens.

Correct Answer: C

Rationale: Rationale: - ARDS is characterized by severe hypoxemia and respiratory distress. - Tachypnea is a hallmark sign of ARDS due to the body's compensatory mechanism to increase oxygenation. - Hypoxemia refractory to supplemental oxygen signifies the inability to improve oxygen levels despite intervention. - Choices A, B, and D do not align with typical manifestations of ARDS, as they do not directly reflect severe hypoxemia or respiratory distress.