This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
[{'content': 'Convulsions in a child with dehydration and vomiting can only be due to – \nSelect and explain. \nA. Decreased serum sodium, B. Decreased serum magnesium, C. Decreased serum potassium, D. Decreased serum potassium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]