This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'In echocardiography pulses of of ultrasonic waves are admitted at a frequency of \nSelect and explain. \nA. 1 megahez, B. 2 megahez, C. 20 Hez, D. 2000 Hez', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In echocardiography pulses of ultrasonic waves at a frequency of 2.25 megahez are admitted from a transducer that also functions as a receiver as a receiver to detect waves reflected back from various pas of the hea. Ref:page no 347 Textbook of physiology Volume 1 AK Jain 7th edition', 'role': 'assistant'}]