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: Ophthalmology
[{'content': 'In colour perimetry the smallest field of vision is with: \nSelect and explain. \nA. Green object, B. Blue object, C. Yellow object, D. Red object', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Green object', 'role': 'assistant'}]