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: Social & Preventive Medicine
[{'content': "What is indicated by the term 'Phon'? \nSelect and explain. \nA. Psycho-acoustic index of loudness, B. Noise induced hearing loss, C. Sound spectrum, D. Octave Band Frequency Analyzer", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Noise may be expressed in psycho-acoustic terms - the phon. The phon is a psyho-acoustic index of loudness. It takes into consideration intensity and frequency. Also remember: "Octave Band Frequency Analyser," which measures the noise in octave bands. The resulting plot shows the "sound spectrum" and indicates the characteristics of the noise, whether it is mainly high-pitched, low-pitched or of variable pitch. Ref: Park\'s textbook of Preventive and Social Medicine, 21stedition, page-684', 'role': 'assistant'}]