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: Gynaecology & Obstetrics
[{'content': 'Which of the following explanations is not an explanation for decreased variability of the fetal hea tracing : \nSelect and explain. \nA. Fetal "sleep state", B. Prematurity, C. Barbiturate ingestion, D. Fetal stimulation', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Fetal stimulation', 'role': 'assistant'}]