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: Dental
[{'content': 'The primary difference between MTA and Portland cement is that, MTA \nSelect and explain. \nA. Lacks potassium, B. lacks Al, C. lacks Mg, D. lacks Fe', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The primary difference between both types of MTA and Portland cement are a lack of potassium and presence of bismuth oxide. White\xa0MTA contains lower amounts of Fe, Al and Mg than grey MTA.\nref. MTA review, JOE 2010, pg 17', 'role': 'assistant'}]