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: Medicine
[{'content': 'Which of the following trace element cannot be completely Supplemented by diet during pregnancy . \nSelect and explain. \nA. Iron, B. Calcium, C. Manganese, D. Zinc', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]